Let me start by saying that Key Lime Pie is among my all-time favorite desserts. So, naturally, I’ve done a fair bit of research to try to find the best for this marvelous concoction. More about that later. First, let’s discuss the difference between Key Lime (Citrus aurantiifolia) and Persian Lime (Citrus latifolia).
Persian limes are the ones commonly sold in the US, grown here and in Mexico, with a balanced flavor and acidity. Key limes are originally native to Southeast Asia, passing through the Middle East to North Africa, Sicily, and Andalucia, and via Spanish explorers, to the West Indies and Florida. Groves of Key Limes used to be in California, Texas, and mainland Florida, but the groves in the Florida Keys took over much of the market in the early 20th century due to the fact that the region’s alkaline soil and abundant coastal rains produced a 2 inch diameter, yellow lemon-like sized fruit that were fat and juicy, with a yellowish thin rind and well-balanced acidity. Unfortunately, a hurricane wiped out many of the groves in 1926, and farmers replaced them with the larger, seedless Persian limes.
What is currently being sold here as Key Limes are grown in Mexico, and the soil there produces a very small, green, seeded, dry and bitter fruit.
Not at all like the fully ripe yellow/green rind and floral juice that made the Key Limes so prized. For a more detailed discussion, here is a link to Stella Park at Serious Eats: https://www.seriouseats.com/2016/05/are-key-limes-worth-the-price.html
I’ve gone the route of buying Key Limes (from Mexico) and being both disappointed and ripped off. I’ve also tried Nettie and Joe’s Key Lime Juice made from concentrate, and that disappoints as well (I also cannot tell you the source of that brand’s Key Lime but I wouldn’t be surprised if their limes were from Mexico). The one thing that is settled is unless you have a source for true Key Limes grown to their full potential, use Persian limes in any of the recipes for “Key Lime” pies or bars.
My research into Key Lime Pie has had some interesting results. One of the most prized recipes is for Ruth Butter’s Key Lime pie, and there is an interesting story there.
Mrs. Butters’ Secret Key Lime Pie Recipe
By Larry Winebrenner | Submitted On August 15, 2005
“Frozen Key Lime Pie recipe?” Fern Butters asked. “Child, I’ll take that secret with me to the grave.”
Fern Butters’ frozen key lime pie was legend. Every time President Harry S Truman went through Islamorada on Upper Matecumbe Key on his way to the “Little White House” in Key West, he stopped. More specifically, he
stopped at Fern Inn for some of Fern Butters’ frozen key lime pie.
And so did other folks, commoners and dignitaries alike-Papa Hemingway, Cordell Hull, Douglas Fairbanks, Julia Child . And me.
I didn’t see any of those famous folks. Except Julia Child. And I didn’t know who she was. Ignorance of youth.
But I did eat Mrs. Butters’ frozen key lime pie.
I wasn’t a child when I asked her about the recipe. I had recipes for my grandmother’s compressed fruit cake. And my grandfather’s elderberry wine. And a passel of others I’d collected from near and far. So I thought her recipe would fit right in with my collection.
Not so. I was a young pastor at her little church in Matecumbe. But I could have been Gabriel himself.
And could never obtain that closely guarded secret.
Many had tried to replicate her recipe, but without success. I saw Julia Child once try to wheedle the recipe from Fern Butters with no success. I heard she tied to duplicate the recipe-again, no success.
Of course, that may just be a legend. It’s believable. Everyone who ever ate her frozen key lime pie coveted the recipe.
Well, Fern is now dead. The Fern Inn has changed names. Fern took the recipe to the grave with her.
But, recently her daughter called me up. She said that after all these years she was going through her mother’s letters and things and trying to clean out an old dresser drawer packed with old letters and notes.
She came across an envelope with my name on it. She wanted to know if I were the same preacher that served the little church down in Matecumbe.
This was a strange event. I had moved to Wisconsin serving churches there for several years. When I returned to South Florida, I was a professor in a college for 33 years. I retired from the college and served a church in North Miami Beach for 13 years. I retired again. Then answered a desperation call to serve as chaplain at a retirement community. I just happened to be in the area where Fern Butters’ daughter could contact me.
She sent me the envelope, now yellow with age. Fern had been dead for some 40 or so years. I opened the envelope. The note read:
This is what you asked for. Use it wisely.
And there was the recipe!
Now I’ve wondered what to do with this recipe. I could, of course, just publish it. Or I could write a book about my days as a young pastor among the Keys Conchs, as the folks there called themselves. I might even sell it [How long would that last!?]
But I’ve decided to give it away. I’m not even going to swear the recipients to secrecy. I’m just going to give it to folks who have a love for unusual recipes and for historical recipes. I have a buddy from North Carolina, for example, whose family has a recipe for pumpkin soup handed down since pioneer days.
With Fern’s secret ingredient [forgive me, Fern!].
Mrs. Butters' Secret Key Lime Pie Recipe
Ingredients
1 Cup sweetened condensed milk
6 egg yolks [save whites]
½ Cup key lime juice [genuine key lime]
6 egg whites [I told you to save them!]
1 Tablespoon cream of tartar
1 Cup sugar
1 graham cracker pie crust [preferred-regular crust permissible]
½ pint secret ingredient (soft vanilla ice cream)
Procedure
Filling
Add yolks to condensed milk and beat 8 minutes
Add secret ingredient and beat until well mixed
Add key lime juice and mix well
Fold into pie shell
Place in freezer until well set. Keep unused portion in the freezer for up to a week [if it lasts that long!]
Topping
While pie sets beat 6 egg whites with cream of tartar for 5 minutes.
Add 1 cup of sugar and whip until meringue makes peaks when beater is removed from mixture.
Add to top of pie
Brown in 350◦ oven and cool in refrigerator for 15 or more minutes for a regular pie or in the freezer for an hour if it is frozen key lime pie.
Now, I wonder if somehow David L. Sloan, a “Key Lime Pie expert” saw this recipe. Featured in Molly O’Neill’s article, “The Curious Case of Key Lime Pie”, Sloan’s recipe is very similar to Larry’s recipe. https://www.epicurious.com/archive/seasonalcooking/winter/key-lime-pie
Epicurious billed it as “the ultimate Key Lime Pie”
David Sloan's Ultimate Key Lime Pie
The end result is pie with a soft and delicate filling reminiscent of Italian semifreddo. Most graham cracker pie shells are baked prior to being filled, but because the pie is frozen after it is baked, it is recommended to skip the pre-bake for a tender, easily cuttable crust.
INGREDIENTS
- For the graham cracker and cereal crust:
- 1 cup graham cracker crumbs from about 8 (2 1/4-inch by 4 3/4-inch) crackers
- 1 cup honey-nut cereal crumbs, such as crushed Honey Nut Cheerios
- 1/4 cup packed light brown sugar
- 7 tablespoons salted sweet cream butter, melted
- 1/2 teaspoon ground cardamom
- For the filling:
- 6 large egg yolks
- 1 (14-ounce) can sweetened condensed milk
- 1 cup vanilla ice cream, softened
- 1/2 cup fresh or bottled Key lime juice
- To serve:
- 1 cup heavy cream
- 3 tablespoons confectioners’ sugar
PREPARATION
- Make the graham cracker and cereal crust:
- Arrange a rack in the middle of the oven and preheat to 350°F.
- Spray a 9-inch pie plate liberally with nonstick vegetable-oil spray.
- In a medium bowl, stir together the graham cracker crumbs, honey-nut cereal crumbs, and brown sugar. Drizzle with the melted butter and stir until well combined. Press the mixture evenly onto the bottom and up the sides of the prepared pie plate and refrigerate for 30 minutes.
- Make the filling:
- In the bowl of a stand mixer fitted with the whisk attachment, beat the egg yolks for 1 minute. Add the sweetened condensed milk and beat until pale and aerated, about 6 minutes. Add the ice cream and beat until smooth then add the lime juice and beat until combined. Pour the filling into the pie shell and bake until just set in the center, about 12 minutes. Transfer to a wire rack to cool completely then freeze until chilled through, at least 1 hour. DO AHEAD: The pie can be baked and kept in the freezer, well wrapped, up to 3 days.
- Garnish and serve:
- Remove the pie from the freezer and thaw in the refrigerator for 20 minutes prior to serving.
- In a medium bowl, combine the heavy cream and sugar and whip until soft peaks form. Cut the pie into slices and top each with a dollop of whipped cream.
Here is a modern version, this one from Joe’s Stone Crab in Miami Beach.
Joe's Stone Crab Key Lime Pie
Ingredients
Graham cracker crust
- 1/3 pound graham crackers (1 cup and 2 1/2 tbs graham cracker crumbs
- 5 tablespoons melted unsalted butter
- 1/3 cup granulated sugar
Filling
- 3 large egg yolks
- 2 large limes, grated to produce 1 ½ teaspoons zest
- 14 ounces (1 can) sweetened condensed milk
- 2/3 cup freshly squeezed lime juice
Topping
- 1 cup heavy cream, well chilled
- 3 tablespoons confectioners sugar
Procedure
- For the graham cracker crust: Preheat the oven to 350 degrees F. Butter a 9-inch pie pan. Break up the graham crackers: place in a food processor and process to crumbs. (If you don’t have a food processor, place the crackers in a large plastic bag: seal and then crush the crackers with a rolling pin). Add the melted butter and sugar and pulse or stir until combined. Press the mixture into the bottom and sides of the pan, forming a neat border around the edge. Bake the crust until set and golden, 8 minutes. Set aside on a wire rack. Leave the oven on.
- For the filling: Meanwhile, in a electric mixer with the wire whisk attachment, beat the egg yolks and lime zest at a high speed until very fluffy, abut 5 minutes. Gradually add the condensed milk and continue to beat until thick, 3 or 4 minutes longer. Lower the mixer speed and slowly add the lime juice, mixing just until combined, no longer. Pour mixture into the pie crust. Bake for 10 minutes, or until the filling has set. Cool on a wire rack, then refrigerate. Freeze for 15 to 20 minutes before serving.
- For the topping: Whip the cream and the confectioners’ sugar until nearly stiff. Cut the pie in wedges and serve very cold, topping each wedge with a large dollop of whipped cream.
Yield: 1 (9-inch) pie Prep Time: 40 minutes Cook Time: 20 minutes
Servings: 8
Preparation Time: 1 hour
If you’re feeling terribly Little-House-on-the-Prairie you can make your own sweetened condensed milk, also known as dulce de leche, by pouring 1 quart whole milk and 1 cup sugar into a large, wide pot. Heat to a simmer. Cook, stirring now and then, until thick, sweet and tan-colored, about 1 ½ hours. The milk should reduce by 60%. The difference between condensed milk and evaporated milk is the addition of the sugar to the evaporated milk. Condensed milk was developed by Gail Borden, Jr. in 1853, and was used as a ration for Union soldiers in the Civil War, as it was stable in a can and required no refrigeration.
Another take is from Pepe’s cafe in Key West, Florida. The addition of egg whites to the filling makes it fluffier than more traditional versions.
Pepe's Cafe Key Lime Pie
Yield 8 servings
Ingredients:
For the graham cracker crust
- 1 1/2 cups graham cracker crumbs (from 12 graham cracker)
- 1/4 cup granulated sugar
- 1 teaspoon ground cinnamon
- 5 tablespoons unsalted butter, melted
For the filling
- 2 large egg whites
- 4 large egg yolks
- 14 ounces (1 can) sweetened condensed milk
- 1/2 cup freshly squeezed Key Lime juice
To serve
- 1 cup heavy cream
- 3 tablespoons confectioners’ sugar
Preparation
Make the crust
- Preheat oven to 350°F
- Mix the graham cracker crumbs, sugar, and cinnamon. Drizzle with the melted butter and stir until well combined. Press the mixture into the bottom and sides of a 9 inch pie plate. Bake until set and golden brown, about 10 minutes. Transfer to a wire rack to cool completely.
Make the filling
- In the bowl of a stand mixer, whisk the egg whites until they hold stiff peaks.
- In a large bowl, whisk the egg yolks with the condensed milk. Add the lime juice and whisk until combined. Gently fold in 1/3 of the egg whites until no white is seen, then add the rest of the egg whites and fold in gently. Spread the mixture into the prepared crust and bake until just set in the center, about 20 minutes. Transfer to a wire rack to cool completely, then refrigerate for at least 2 hours prior to serving.
To serve, combine the heavy cream and sugar and whisk until soft peaks form. Use the sweetened cream to top each slice of pie.
Here’s a version of the pie that doesn’t use the standard sweetened condensed milk. Adapted from “Allen Susser’s New World Cuisine and Cookery.”
Key Lime pie using Lime Curd
Crust
- 1 ½ cups graham cracker crumbs
- ½ cup ground pecans
- 3 tablespoons sugar
- 1/3 cup unsalted butter, melted
Curd
- Juice of 9 Key limes, about 3/4 cup
- 1 cup heavy cream, whipped to soft peaks
Procedure
Heat oven to 350 degrees. Mix graham cracker crumbs, pecans and sugar in 9-inch pie pan. Stir in melted butter. Mold crumbs against sides and bottom of pan. Bake 4 minutes. Cool; chill in refrigerator.
For curd, heat sugar, butter and lime juice in top of double boiler over low heat. Cook, stirring, until butter melts. Whisk in eggs; cook until mixture is thick enough to coat back of spoon, about 5 minutes. Transfer to stainless-steel bowl placed in another bowl filled with ice to chill, stirring constantly.
-
Spoon curd into crust. Cover with plastic wrap set directly on top of curd. Refrigerate 2 hours before serving. However, needs to freeze to set up properly, so freeze for at least 15 minutes prior to serving, and serve semi-frozen to preserve integrity of pie slices. Serve with whipped cream, either on the side or on top.
Not done yet, here are more variations. This one is from Michelle Norris (aka the BrowneyedBaker).
Key Lime Pie with a better crust
Quick and easy key lime pie recipe starts with a graham cracker crust and filling of egg yolks, sweetened condensed milk, key lime juice & zest.
FOR THE LIME FILLING:
- 4 teaspoons grated key lime zest
- 4 egg yolks
- 14 ounces sweetened condensed milk
- ½ cup fresh key lime juice
FOR THE GRAHAM CRACKER CRUST:
- 2 cups graham cracker crumbs(approximately 14 full graham crackers)
- 1/3 cup light brown sugar
- 1/2 cup unsalted butter (melted)
- Pinch salt
FOR THE WHIPPED CREAM TOPPING:
- 1½ cups heavy cream (chilled)
- ½ cup powdered sugar
-
Preheat oven to 350 degrees F.
-
Make the Filling: Whisk the lime zest and egg yolks together in a medium bowl for 2 minutes. Whisk in the sweetened condensed milk, then the lime juice. Set aside at room temperature to thicken while you prepare the crust.
-
Make the Crust: In a medium bowl, stir together the graham cracker crumbs, brown sugar, and salt, ensuring no lumps of brown sugar remain. Drizzle the melted butter over the graham cracker mixture and toss to combine with a fork, ensuring that the mixture is evenly moistened. Press the crust mixture evenly into the bottom and up the sides of a 9-inch pie plate, and pack tightly using the back of a measuring cup. Bake for 10 minutes; transfer to a wire rack to cool to room temperature.
-
Once the crust has cooled to room temperature, pour the lime filling into the crust. Bake until the center is set, yet still wiggly when jiggled, 15 to 17 minutes. Return the pie to a wire rack; cool to room temperature. Refrigerate until well-chilled, at least 3 hours. (At this point, the pie can be covered directly with plastic wrap sprayed with non-stick cooking spray and refrigerated for up to 1 day.)
-
Make the Whipped Cream: Using an electric mixer, whip the cream on medium speed until soft peaks form. At this point, add the powdered sugar, 1 tablespoon at a time, while continuing to whip the cream until stiff peaks form. Decoratively pipe the whipped cream over the filling or spread the whipped cream evenly with a spatula. Garnish with lime slices, if desired, and serve. Cover leftovers with plastic wrap and refrigerate for up to 3 days.
Michelle makes the point that her crust is different, using light brown sugar instead of granulated. As a variation, she also suggests using browned butter to enhance a nutty flavor. She claims the crust is perfectly moist and holds together without leaking due to too much butter. The brown sugar elevates the crust in taste compared to using granulated sugar. With the correct packing in of the crust, the result will give a crust that gives that gives a clean slice every time.
I found when I made Michelle’s crust that I did not have enough butter to adequately moisten the amount of graham crackers. You must be able to shape the crust with a little pressure, and that requires enough butter. Also, not mentioned in her recipe, it is vital to grease the pie pan with enough butter so that the crust can separate from the bottom of the pan when you cut the pie slices.
Here is one from Deb Perelman (aka the Smitten Kitchen)
an adaption of Joe's Key Lime Pie
Classic Key Lime Pie
Adapted somewhat liberally from the version at Joe’s Stone Crab in Miami, where I am not.
Every key lime pie recipe agrees that a can of sweetened condensed milk is the king of ingredients. From there, they diverge. Some use more lime juice, some less. (I use 2/3 cup for a nicely tart filling; use only 1/2 cup if you’re more wary of the tartness of limes.) Some use more egg yolks, some use less. (I find I only need 3 for a good set and flavor, but you can go up to 5 if you’d like something extra-rich.) Not all insist that you whip your yolks until they’re pale and ribbony, but it makes for a lovely final texture and I think is worth it.
Most importantly, despite the name, you don’t need key limes to make this. I mean, if you can get them, please do. They’re wonderful. But I made this, as I often do, with regular grocery store Persian limes and it’s no less dreamy with them.
Crust
1 1/2 cups (155 grams) finely ground graham cracker crumbs (from about 10 crackers)
3 tablespoons (40 grams) granulated sugar
2 pinches sea salt
7 tablespoons (100 grams) unsalted butter, melted
Filling
1 1/2 tablespoons finely grated lime zest
3 large egg yolks (though extra-large would do you no harm here)
1 14-ounce (396-gram) can sweetened condensed milk
2/3 cup (155 ml) fresh lime juice (from about 1 dozen tiny key limes or 4 persian/regular limes)
To Finish
3/4 cup (175 ml) heavy whipping cream
1 to 2 tablespoons powdered or granulated sugar, to taste
Heat oven: To 350°F (176°C).
Make crust: Combine graham crumbs, sugar and salt in a medium bowl and stir until mixed. Add butter and stir until crumbs are evenly coated. SDR note: liberally butter the bottom and sides of the pie pan. Press crumbs into the bottom and up the sides of a standard 9-inch pie dish. I like to use the outer edge of a heavy measuring cup to press in neat, firm sides but nobody will be the wiser if you just use your fingertips. Bake crust until lightly browned, about 10 minutes. Set on cooling rack while you prepare filling. Leave oven on.
Make filling: Zest limes into the bottom of a medium bowl until you have 1 1/2 tablespoons. Beat zest and egg yolks with an electric mixer until pale and thick, about 5 minutes. Add sweetened condensed milk and beat until thickened again, about 3 minutes more. Squeeze zested limes until you have 2/3 cups juice. Depending on the size of the limes, you will need from 4 to 6 Persian limes to get enough juice. Whisk into yolk mixture until combined. Pour into graham crust and bake pie for another 10 minutes, until set but not browned on top at all. Let pie cool completely before adding topping — you can do this outside (thank you, January!) or even in your freezer (but don’t forget about it) to hasten the process, and your pie reward, along.
Make topping: In a medium bowl, beat cream and sugar until soft peaks are formed. Spread over top of chilled pie. Ideally, pie should be chilled at least another 2 to 3 hours with the cream on top so that it can fully set before you take a slice, but whether that happens is between you and your pie.
Key lime pie keeps in fridge for a week, though certainly not around here.
Deb’s variation produces a wonderfully tart concoction of a dessert. Having some whipped cream on top will cut the tartness as a nice counterpoint.
I will let Stella Parks have the last crack at the best key lime pie. Here is her pie…
Creamy Lime Pie
This pie relies on the killer combo of citrus and dairy (think Creamsicle) for a mellow, sweet, and sour dessert. The crispy whole wheat crust underscores the zippy custard with its graham-like flavor, while fluffy peaks of toasted meringue recall those of a classic lemon meringue pie. It all comes together in a pie that tastes both familiar and distinctive at the same time.
Why It Works
- Milk softens the sour edge of lime, for a filling that’s creamy and tart but mellow.
- Using whole eggs keeps the custard light and the lime flavor fresh and bright.
- A few drops of rosewater bring a fresh aroma to the cooked custard filling.
- A crisp whole wheat crust gives the pie a hearty, graham cracker–like vibe.
- Oven-browned meringue puffs as it bakes, for a lighter texture than meringue browned with a torch.
- YIELD:Makes one (9-inch) pie
- ACTIVE TIME:About 45 minutes (with a prebaked crust)
- TOTAL TIME:5 hours (with a prebaked crust)
Ingredients
- 1/2 recipe Whole Wheat Pie Crust, blind-baked according to recipe directions
- For the Filling:
- 9 ounces sugar (shy 1 1/3 cups; 255g)
- 1 1/2 ounces cornstarch (about 1/3 cup plus 1 tablespoon; 42g)
- 1/4 teaspoon (1g) Diamond Crystal kosher salt; for table salt, use about half as much by volume or the same weight
- 4 large eggs (about 7 ounces; 195g)
- 1/4 ounce lime zest (about 2 tablespoons; 7g), from about 4 limes (see note)
- 8 ounces fresh lime juice (about 1 cup; 225g), from about 8 limes (see note)
- 16 ounces milk, any percentage will do (about 2 cups; 455g)
- 1/4 teaspoon rosewater(optional)
- For the Topping:
- Swiss Meringue, full or half batch as desired
Directions
-
Getting Ready: In a 9-inch glass pie dish, prepare and blind-bake the whole wheat pie crust according to the directions in the recipe. This can be done up to a week in advance; crust can be held at room temperature if wrapped tightly in plastic.
-
For the Filling: In a 3-quart stainless steel saucier, combine sugar, cornstarch, and salt and mix until smooth, then whisk in eggs, lime zest, and lime juice, followed by milk. Cook over medium-low heat, whisking constantly but gently, until hot to the touch, about 5 minutes.
-
Increase heat to medium and continue whisking until thick, about 3 minutes longer. When custard begins to bubble, set a timer and continue whisking for exactly 2 minutes. (This is important to neutralize a starch-dissolving protein found in egg yolks.) Remove from heat and stir in rosewater, if using. Pour into prepared pie crust. For a silkier texture, first strain through a stainless steel sieve, pushing the thick custard through with a flexible spatula.
-
For the Topping: Adjust oven rack to lower-middle position and preheat to 375°F (190°C). Prepare Swiss Meringue as directed, making a half or full batch depending on your own personal preference for meringue. Transfer to a piping bag fitted with a large star tip. Starting at the very edge of the pie, pipe meringue kisses over surface of custard until completely covered. Alternatively, spread meringue over custard with the back of a spoon. Place on a wire rack set inside a half sheet pan (this setup minimizes heat transfer to the custard) and bake pie until meringue is well browned, about 15 minutes.
-
To Serve: Cool pie to room temperature, then cover loosely in plastic and refrigerate until no warmer than 60°F (16°C), about 3 1/2 hours. Cut with a wet chef’s knife, rinsing the blade clean with cold water between slices. Wrapped in plastic, leftovers can be refrigerated up to 1 week.
All of the recipes are slightly different, so decide which is best!
Transfer to a bowl and melt the ½ cup of butter, and mix thoroughly. 
Press the mixture into the baking pan, using a spatula and a flat surfaced measuring cup to evenly spread the crumb mixture.
Pour the condensed milk into the bowl and mix thoroughly with a spatula.
Pour the mixture into the prepared pan.
Since you want everything to mix together well, that is why I elected to mix the coconut flakes, pecans and chocolate together first, and then added the condensed milk to bind everything together (rather than a layer of condensed milk, topped with chocolate first, coconut second, and finally pecans). This is a very intense bar and a small serving is enough.
