Graham Cracker Crust: Preheat oven to 350F (180C). Mix graham cracker crumbs, sugar, and melted butter in a small bowl. Pour crumb mixture into an 8" - 9.5" pie pan and press it firmly in the bottom of the pan and a little bit up the sides of the pan. Bake for 10 minutes. Remove from oven and allow to cool.

Key Lime Filling: Add cream cheese to a mixing bowl and beat well with electric beaters until smooth. Add both cans of sweetened condensed milk, lime juice, and lime zest and mix again until smooth. Pour into prepared graham cracker crust.

Bake in preheated oven for 10 minutes. Allow pie to cool for about 30 minutes, then refrigerate for at least 3 hours, before serving.

Whipped Cream Toppings: Add heavy cream to a mixing bowl and beat with electric mixers for 1 minute. Slowly add powdered sugar and vanilla and continue beating until stiff peaks form. Spread or pipe the whipped cream on top of the cooled pie.