Preheat the oven to 350°F (175°C)
Mix graham cracker crumbs, melted butter, and sugar
Press the mixture into a pie dish
Bake the crust for 8 to 10 minutes
Let the crust cool
Whisk sweetened condensed milk, egg yolks, lime juice, and lime zest
Pour the filling into the cooled crust
Bake for 15 to 18 minutes
Let the pie cool to room temperature
Chill the pie in the refrigerator for at least 3 hours
Top with whipped cream if desired
Slice and serve