Preheat the oven to 350°F (175°C).
In a bowl, combine graham cracker crumbs, melted butter, and sugar.
Press the mixture into the bottom and sides of a pie dish.
Bake the crust for 10 minutes until golden.
In another bowl, whisk egg yolks until thick and pale.
Add sweetened condensed milk and mix until smooth.
Stir in key lime juice and lime zest.
Pour the filling into the baked crust.
Bake for an additional 15 minutes until set.
Cool and refrigerate for at least 3 hours before serving.