Combine the graham cracker crumbs and sugar. Stir in the melted butter until thoroughly combined and moistened.

Press the mixture evenly into the bottom of the prepared pan.

Bake the crust for 10 minutes, or until lightly golden. Remove from the oven and let it cool while you make the filling.

In a large mixing bowl, whisk together the egg yolks and sweetened condensed milk until smooth. Gradually whisk in the key lime juice until well combined. Then, stir in the key lime zest until evenly distributed.

Pour the filling mixture over the baked crust, spreading it evenly.

Bake for 20 minutes or until the filling is set with a slight jiggle in the center.

Cool the bars completely.

In a large mixing bowl, whip the heavy cream, confectioners' sugar, and vanilla extract until stiff peaks form.

Spread the whipped cream evenly over the top of the bars.

Refrigerate the bars for at least 2 hours, or until the cream topping is set.

Use the overhanging parchment to lift the bars out of the pan and onto a cutting board. Cut into bars. Garnish with additional key lime zest before serving.