Preheat your oven to 350°F (175°C). In a medium bowl, combine graham cracker crumbs, granulated sugar, and melted butter. Mix until well combined. Press the mixture firmly into the bottom and up the sides of a 9-inch pie pan to form the crust. Bake for 8-10 minutes or until lightly golden. Remove from the oven and let cool completely.

In a separate bowl, whisk together the sweetened condensed milk, sour cream, key lime juice, and vanilla extract until smooth and well combined. Pour this mixture into the cooled graham cracker crust.

Bake the pie for an additional 10-12 minutes, then remove from the oven and let it cool to room temperature. Once cooled, refrigerate for at least 2 hours to set.

In a mixing bowl, whip the heavy cream and powdered sugar together until stiff peaks form. Spread or pipe the whipped cream over the chilled pie.

Garnish with lime zest if desired. Slice and serve chilled.