Make the Crust:
Preheat your oven to 350°F (175°C). In a medium bowl, mix the graham cracker crumbs, granulated sugar, melted butter, and vanilla extract until the crumbs are evenly coated. Press the mixture firmly into the bottom and up the sides of a 9-inch pie dish. Bake the crust in the preheated oven for about 8-10 minutes, or until lightly golden and set. Remove from the oven and let cool while you prepare the filling.

Make the Filling:
In a large mixing bowl, whisk together the sweetened condensed milk, key lime juice, and egg yolks. Whisk until smooth and well combined. If you want a stronger lime flavor, add the zest of one key lime to the filling. Pour the filling into the cooled graham cracker crust.

Bake the Pie:
Bake the pie in the oven for 15-17 minutes, or until the filling is set and slightly puffed around the edges (it should still jiggle slightly in the center). Remove from the oven and allow it to cool to room temperature. Once cooled, transfer the pie to the refrigerator and chill for at least 3 hours or overnight for the best texture.

Make the Whipped Cream Topping:
In a medium bowl, beat the heavy cream, powdered sugar, and vanilla extract together until soft peaks form. Spread the whipped cream over the chilled pie, or pipe it on using a piping bag for a decorative touch.

Serve:
Slice and serve the Key Lime Pie chilled. Garnish with extra lime zest or lime slices if desired.