Preheat the oven to 325°F. Line a 9×13-inch baking pan with parchment paper, leaving an overhang for easy removal.

Combine the graham cracker crumbs, granulated sugar, ground cinnamon, and melted butter until evenly moistened. Press firmly into the bottom of the prepared pan.

Bake the crust for 8–10 minutes, until lightly golden. Let it cool for 10 minutes with the pan on a rack.

Beat the cream cheese and granulated sugar until smooth and creamy, about 2 minutes. Scrape the sides and bottom of the bowl to remove lumps (visual cue: silky batter).

Mix in the eggs one at a time, followed by the vanilla extract. Stir until just combined (visual cue: batter looks uniform, not frothy).

Transfer half of the cheesecake mixture to a separate bowl. Keep the remaining half in the original bowl.

Stir the pumpkin purée, pumpkin pie spice, ground cinnamon, ground nutmeg, and flour into one bowl of cheesecake mixture until smooth. Mix just until no dry flour remains (visual cue: thick, spiced pumpkin batter).

Spread the plain cheesecake mixture evenly over the cooled crust. Use a spatula to smooth the surface (visual cue: even top layer).

Spoon the pumpkin cheesecake mixture over the top. Gently swirl the two layers together with a butter knife to create a marbled pattern.

Bake for 38–45 minutes, until the edges are set and the center has a slight jiggle. Turn the pan halfway through if your oven has hot spots (visual cue: center jiggles like set gelatin).

Cool to room temperature, about 45 minutes. Cover lightly once cool to prevent condensation.

Refrigerate for at least 4 hours or overnight until fully chilled. For clean slices, chill until the bars feel firm all the way through.

Lift the bars from the pan using the parchment paper. Place on a cutting board and peel away parchment for a neat edge.

Slice into squares and serve chilled. Wipe the knife between cuts for crisp lines.