1/2 cup key lime juice (preferably fresh, but bottled juice also works)
(optional topping) 2 cups whipped cream
To Make The Graham Cracker Crust:
Preheat oven to 350°F.
Stir together graham cracker crumbs, sugar, and butter in a bowl until evenly combined. Press mixture evenly onto bottom and up side of a 9-inch (4-cup) pie plate. Bake crust on the middle oven shelf for 10 minutes, then remove and let cool.
To Make The Filling:
While the crust is baking, whisk together the condensed milk and egg yolks in a bowl until combined. Add juice and whisk by hand for 1 minute until combined and slightly thickened.
Pour filling into crust and bake on the middle oven shelf for 15 minutes. Transfer pie to a cooling rack, and let sit until it reaches room temperature. Then refrigerate for at least 3 hours, or until chilled and set.
Top with whipped cream just before serving, if desired