Preheat the oven to 350°F (175°C).

In a mixing bowl, combine graham cracker crumbs, granulated sugar, and melted butter. Mix until well combined.

Press the mixture into the bottom and up the sides of a mini muffin tin to form small crusts.

Bake in the preheated oven for 8-10 minutes until lightly golden. Remove and let cool.

In another bowl, whisk together egg yolks, sweetened condensed milk, key lime juice, and lime zest until smooth.

Pour the filling into the cooled crusts, filling each about 3/4 full.

Bake for an additional 5-7 minutes until the filling is set. Remove from oven and let cool completely.

In a mixing bowl, beat the chilled heavy whipping cream with powdered sugar and vanilla extract until soft peaks form.

Pipe or spoon the whipped cream onto each mini pie.

Garnish with additional lime zest if desired and serve chilled.