Preheat your oven to 350°F (175°C). In a bowl, combine graham cracker crumbs, sugar, and melted butter. Press the mixture into the bottom and up the sides of a 9-inch pie dish. Bake for 8-10 minutes until golden brown. Allow it to cool completely.
In a large bowl, whisk the egg yolks until pale and slightly thickened. Add the sweetened condensed milk, key lime juice, and key lime zest. Mix until well combined. Pour the filling into the cooled graham cracker crust.
Bake the pie for 15 minutes at 350°F (175°C) until the edges are set but the center is slightly jiggly. Allow the pie to cool at room temperature, then refrigerate for at least 4 hours or overnight to set.
In a chilled bowl, whip the heavy whipping cream until soft peaks form. Add powdered sugar and vanilla extract. Continue whipping until stiff peaks form.
Spread the whipped cream over the chilled pie. Garnish with additional key lime zest for a burst of color and flavor.
Use a sharp knife to slice through the creamy goodness and the crumbly crust. Serve chilled and savor the Southern sunshine in every bite.