Preheat the oven to 350°F (177°C). Line a 12-count muffin pan with liners and a second 12-count muffin pan with only 4 (since this recipe makes only around 16). Set pans aside.
Make the crust: Mix the graham cracker crumbs, melted butter, and granulated sugar together with a silicone spatula in a medium bowl until combined. Press a heaping Tablespoon of mixture down into each liner, making sure the crust is tight and compact. Pre-bake the crusts for 5 minutes. Remove from the oven.
Make the filling: In a large bowl using a handheld or stand mixer fitted with a whisk attachment, beat the cream cheese on high speed until smooth, about 1 minute. On medium-high speed, beat in the egg yolks. On high speed, beat in the sweetened condensed milk and lime juice until combined.
Pour the filling evenly into each crust. Bake for 15–16 minutes or until the centers of the pies only slightly jiggle. Allow the pies to cool at room temperature in the pan set on a wire rack. Once completely cool, place the pan in the refrigerator for at least 2 hours and up to 1 day.
Once chilled, serve the key lime pies cold with whipped cream and a lime slice if desired. Store leftover pies in the refrigerator (covered) for up to 1 week.
