Preheat the oven to 325℉. Line a 9-inch square pan with parchment paper, letting the foil hang over the sides of the pan.

Mix together the melted butter, brown sugar, cardamom, and graham cracker crumbs. Pat the mixture down into the prepared pan to form a crust. Bake in the preheated oven for 10 minutes.

In a large bowl using an electric handheld mixer, beat together the cream cheese and brown sugar on high speed for 1 minute. Add the eggs, nutmeg, salt, vanilla, and rum extract and beat on medium speed for 30 seconds. Add the eggnog and beat for another 30 seconds.

Pour the filling over top of the baked crust and then bake for another 35-40 minutes. The edges should be slightly golden brown and the center should be almost set. Place the pan on a wire rack to cool to room temperature for 1 hour before moving to the refrigerator to chill for at least another 3 hours or until fully chilled.

When ready to serve, pull the bars out of the pan using the overhanging parchment paper as a handle and slice into 16 bars using a sharp knife. Rinse the knife with hot water and wipe dry between each cut for clean-edged bars. Serve with whipped cream. Enjoy!