Preheat your oven to 350°F (175°C).

In a bowl, combine the graham cracker crumbs with the melted butter. Mix until it resembles wet sand.

Press this mixture firmly into the bottom of a greased 9×9-inch baking dish to form a sturdy crust.

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

Pour the lime mixture over the prepared crust, ensuring an even distribution.

Bake for about 15-20 minutes or until the filling is set and slightly jiggles in the center.

Once baked, let the bars cool completely in the pan. Pop them in the fridge for at least 2 hours before slicing.

Serve chilled, dusted with powdered sugar.