Based on a recipe from Florida Keys Cooking pamphlet, published in 1946 by Patricia's Notebook newsletter, this pie is not the ordinarily dense and cloyingly sweet version. Folding in beaten egg whites gives it a light, mousselike texture. The pie needs to chill overnight, so plan accordingly.
How to Make the Ultimate Umami-Bomb Vegetarian Demi-Glace
1 1/2 cups graham cracker crumbs
4 tablespoons unsalted butter, melted
3 large eggs, separated
1 large egg, lightly beaten
One 14-ounce can sweetened condensed milk
1/3 cup fresh lime juice, preferably made from Key limes
1/2 teaspoon finely grated lime zest, plus more for garnish
Sweetened whipped cream, for serving
Preheat the oven to 325°. In a medium bowl, mix the graham cracker crumbs and melted butter. Press the crumbs evenly over the bottom and up the sides of a 9-inch glass pie plate. Bake the crust for about 15 minutes, or until firm. Let cool.
In a large bowl, whisk the 3 egg yolks with the lightly beaten whole egg until thickened. Beat in the condensed milk, then beat in the lime juice and zest.
In a large stainless steel bowl, beat the egg whites until firm peaks form. Fold one-third of the beaten whites into the custard, then fold in the remaining whites. Pour the custard into the pie crust and bake for 15 minutes, or until barely set. Transfer to a rack and let cool completely, then refrigerate over-night. Serve with sweetened whipped cream and garnish with lime zest.