Preheat your oven to 325°F (160°C). Line a 9×13-inch baking pan with parchment paper, leaving an overhang on the long sides for easy lifting. Lightly coat the parchment and any exposed pan sides with nonstick spray.

In a medium bowl, combine the graham cracker crumbs, 2 tablespoons granulated sugar, 1/2 teaspoon ground cinnamon (if using), and a pinch of fine sea salt. Stir to mix evenly. Pour in the melted butter and mix until all the crumbs are evenly moistened and the mixture resembles damp sand. If it seems dry, add another tablespoon of melted butter.

Transfer the crumb mixture to the prepared pan. Use the bottom of a measuring cup or a flat glass to press the crumbs firmly and evenly across the bottom of the pan, pressing well into the corners. Bake at 325°F (160°C) for 10 minutes. Remove from the oven and set aside while you prepare the filling.

In a large mixing bowl or the bowl of a stand mixer, beat the softened cream cheese on medium speed for 2–3 minutes, until very smooth and fluffy. Scrape down the sides of the bowl. Add 1 cup granulated sugar and beat again until well combined and no grainy texture remains.

Add the eggs one at a time, beating on low speed after each addition just until blended. Avoid overbeating to prevent incorporating too much air, which can cause cracks.

Add the eggnog, vanilla extract, ground nutmeg, ground cinnamon, flour, and salt. Beat on low speed until the batter is smooth and everything is fully incorporated. Scrape the bowl and give it one last quick mix. The batter should be silky and pourable—thicker than heavy cream but looser than cake batter.

Pour the eggnog cheesecake filling evenly over the warm or slightly cooled graham cracker crust. Use a spatula to smooth the top. Tap the pan gently on the counter a few times to release any large air bubbles. Bake at 325°F (160°C) for 35–45 minutes, or until the edges are set and slightly puffed and the center still has a slight wobble when you gently jiggle the pan, like nearly set gelatin. If the edges begin to brown too quickly, loosely tent the pan with foil during the last 10 minutes.

Turn off the oven, crack the oven door, and let the pan sit inside for 15 minutes to cool gradually and help prevent cracks. Remove the pan to a wire rack and let the cheesecake cool to room temperature, about 1–2 hours.

Once cooled to room temperature, cover the pan or wrap it well and refrigerate for at least 4 hours, preferably overnight. The texture improves and the bars slice more cleanly after a thorough chill.

When ready to serve, lift the chilled cheesecake slab out of the pan using the parchment overhang and place it on a cutting board. Use a sharp knife to cut into 16 large bars or 20–24 smaller squares, wiping the knife clean between cuts for neat edges. Top each bar with a swirl of whipped cream and a sprinkle of nutmeg or crushed gingersnaps, if desired.