01 - Preheat oven to 350°F.
02 - In a medium bowl, combine graham cracker crumbs, sugar, and melted butter. Mix until evenly moistened.
03 - Press mixture firmly into the bottom and up the sides of a 9-inch pie dish.
04 - Bake crust for 8 minutes. Remove and let cool slightly.
05 - In a large bowl, whisk together sweetened condensed milk, egg yolks, key lime juice, lime zest, salt, and a few drops of green food coloring until smooth and evenly colored.
06 - Pour filling into the cooled crust and smooth the top.
07 - Bake for 7 minutes, until the center is just set but still slightly jiggly.
08 - Cool at room temperature for 30 minutes, then refrigerate for at least 4 hours, or until fully chilled and set.
09 - Before serving, whip the cream with powdered sugar and vanilla extract to soft peaks.
10 - Spread or pipe whipped cream over the pie, then garnish with lime zest or slices.