Preheat your oven to 350°F (175°C). Line a 9x9 inch baking pan with parchment paper, leaving an overhang on two sides to easily lift the bars out later.

In a medium bowl, combine graham cracker crumbs, 1/4 cup granulated sugar, ground cinnamon, and 1/4 tsp ground nutmeg. Stir well to combine.

Pour the melted butter over the crumb mixture and stir until fully moistened and well combined. Press the mixture evenly into the bottom of the prepared baking pan. You can use the bottom of a glass or your fingers to get a firm, even layer.

Bake the crust for 8-10 minutes, or until lightly golden and fragrant. Remove from the oven and set aside to cool while you prepare the filling. Reduce oven temperature to 325°F (160°C).

In a large mixing bowl, using a stand mixer with the paddle attachment (or an electric hand mixer), beat the softened cream cheese on medium speed until smooth and creamy, about 2-3 minutes. Scrape down the sides of the bowl as needed.

Add 3/4 cup granulated sugar and all-purpose flour to the cream cheese. Beat on low speed until just combined, then increase to medium and beat for another minute until smooth and no lumps remain.

Gradually beat in the eggnog, rum extract, vanilla extract, and 1/2 tsp ground nutmeg until thoroughly incorporated. The mixture will be a bit thinner.

Add the eggs one at a time, beating on low speed only until each egg is just incorporated. Do not overmix after adding the eggs, as this can lead to cracks in the cheesecake.

Pour the cheesecake filling evenly over the pre-baked graham cracker crust in the pan. Gently tap the pan on the counter a few times to release any air bubbles.

Bake for 35-45 minutes at 325°F (160°C), or until the edges are set and lightly golden, but the center still has a slight jiggle when gently shaken. Turn off the oven, prop the oven door open slightly with a wooden spoon, and let the cheesecake cool in the oven for 30 minutes. This slow cooling helps prevent cracking.

Remove the pan from the oven and let it cool completely on a wire rack at room temperature for at least 1-2 hours. Once cooled, cover the pan loosely with plastic wrap and refrigerate for at least 4 hours, or preferably overnight, to allow the cheesecake to set fully.

Once chilled, lift the cheesecake out of the pan using the parchment paper overhang. Carefully peel away the parchment paper.

In a clean, cold mixing bowl, combine the very cold heavy cream, powdered sugar, and 1 tbsp eggnog. Beat on medium-high speed until stiff peaks form.

Spread the eggnog whipped cream evenly over the chilled cheesecake. Slice into 16 bars (4x4 cuts) using a sharp knife, wiping the knife clean between each cut for neat edges. Dust lightly with ground nutmeg before serving.