To make the graham cracker crust: Preheat the oven to 350°F (177°C).

Line an 8-inch square pan with parchment paper or aluminum foil, leaving some overhang for easy removal, and set aside.

Combine the graham cracker crumbs and sugar in a mixing bowl and mix until well combined. Add the melted butter and stir until fully combined and all of the crumbs are moistened.

Scoop the mixture into the prepared pan and firmly press it down into one even layer. I prefer to use the bottom of a measuring cup to help press the crust into the pan.

Bake for 8 to 10 minutes. Remove from the oven and set aside to cool for 10 minutes while you make the filling.

Reduce the oven temperature to 325°F (163°C).

To make the key lime pie filling: In the bowl of a stand mixer fitted with the paddle attachment, or in a large mixing bowl using a handheld mixer, beat the cream cheese on low-medium speed until smooth. Add the egg yolks and continue mixing until fully combined, stopping to scrape down the sides of the bowl as needed.

Mix in the sweetened condensed milk until well combined, then mix in the key lime juice until fully combined. If needed, use a rubber spatula to turn the filling a few times to make sure everything is thoroughly mixed together.

Pour the filling into the slightly cooled graham cracker crust and smooth it out into one even layer.

Bake for 35 to 40 minutes or until the edges of the filling are set, but the center is still slightly jiggy.

Remove from the oven and allow to cool completely on a wire rack at room temperature, about 2 hours. Once cooled, cover tightly and refrigerate for at least 4 hours or until the bars are thoroughly chilled and firm.

Top with whipped cream before slicing and serving or refrigerate until ready to serve.