Preheat the oven to 350°F. Line an 8x8 inch square baking pan with parchment paper, leaving overhang on two sides for easy lifting.

In a small bowl, combine graham cracker crumbs, brown sugar, and melted butter, mixing until the texture resembles damp sand. Press the mixture evenly into the bottom of the prepared pan. Bake for 10 minutes, or until the crust is lightly golden and set. Remove from the oven and let it cool completely. Reduce the oven temperature to 300°F.

In a medium bowl, beat cream cheese until smooth. Then, add the sweetened condensed milk to the cream cheese and whisk periodically as you pour the milk. Next, whisk in egg yolks, sugar, vanilla, lime juice, and 1 tablespoon of lime zest until smooth. Carefully pour the filling over the cooled crust, spreading it evenly.

Return the pan to the oven and bake at 300°F for 30–35 minutes, until the filling is just set in the center but still has a jiggle like jell-o. Don’t over bake. Place the pan on a wire rack and let it cool completely, about 2 hours.

Cover and refrigerate for at least 3 hours before slicing and serving. Use the parchment lining to lift the bars out of the pan for easier cutting.

Prepare the topping: using a hand mixer, beat the heavy cream, powdered sugar, and vanilla in a medium bowl on medium-high speed until peaks form. Spread the whipped cream evenly over the bars and, if desired, finish with a sprinkle of lime zest and enjoy!