Preheat oven to 350°F (177°C). Line a 9-inch square baking pan with parchment paper, leaving an overhang on the sides to easily lift the bars out of the pan. Set aside.

Make the crust: If you’re starting out with full graham crackers, use a food processor or blender to grind them into fine crumbs. You can also place them in a zip-top bag and crush them into fine crumbs with a rolling pin. Stir the graham cracker crumbs and granulated sugar together in a medium bowl, and then stir in the melted butter. Press into the bottom of the lined pan.

Prebake crust: Bake the crust for 10 minutes. Cool for a few minutes as you prepare the filling.

Make the filling: Using a handheld or stand mixer fitted with a paddle or whisk attachment, beat the cream cheese on medium-high speed until smooth, about 1 minute. Beat in the egg yolks. Scrape down the sides of the bowl as needed. Beat in the sweetened condensed milk, key lime juice, and lime zest until combined. Give it a final whisk by hand to make sure there are no lumps.

Pour/spoon filling evenly onto the warm crust.

Bake for about 18-20 minutes, or until the edges of the bars appear set and the center is only slightly jiggly.

Remove from the oven and allow to cool for 30 minutes on a wire rack, then chill in the refrigerator for at least 2-3 hours.

Lift the parchment paper out of the pan and cut into squares. Garnish with whipped cream, lime slices, and/or extra lime zest if desired.

The bars stay fresh in an airtight container in the refrigerator for up to 5 days.