Preheat oven to 350°F (175°C).
In a bowl, mix graham cracker crumbs, sugar, and melted butter. Press into a 9-inch pie dish to form the crust.
Bake crust for 8 minutes. Remove and let cool.
In another bowl, whisk egg yolks until thick. Add sweetened condensed milk, lime juice, and zest. Mix until smooth.
Pour the filling into the cooled crust. Bake for 15 minutes.
Let pie cool at room temperature, then refrigerate for at least 3 hours or overnight.
Before serving, whip heavy cream with powdered sugar and vanilla extract until stiff peaks form.
Top pie with whipped cream and additional lime zest if desired.