Note: I scaled the recipe up to make two pies.
2 x 9″ graham cracker pie shell
2 cans (14-oz) sweetened condensed milk
11 large egg yolks
9.3 oz fresh Key Lime juice (2/3 c + 4 oz)
Single pie: 1 pie shell, 1 can sweetened condensed milk, 6 large egg yolks, and 2/3 c key lime juice
Heat the oven to 325F.
Use an electric mixer on medium to beat together the sweetened condensed milk, egg yolks, and lime juice just until well-combined.
Spoon the mixture into two pie shells and bake for 20 minutes, until the filling is set (jiggles only slightly when shaken).
Cool the pies completely on a wire rack, then chill in refrigerator for several hours before serving. Serve with whipped cream.
Source: Modified a recipe from Top Secret Recipes by Todd Wilbur, via RecipeZaar