Preheat your oven to 350°F. Line an 8x8-inch baking pan with parchment paper, leaving a little overhang on the sides to make lifting the bars out easier later. Set aside.

In a medium mixing bowl, stir together the graham cracker crumbs, brown sugar, and melted butter. Mix until the crumbs are evenly coated and the texture resembles damp sand.

Press the crumb mixture firmly and evenly into the bottom of the prepared pan to form the crust.

Bake the crust for 10 minutes, then remove from the oven and set aside to cool slightly. Lower the oven temperature to 325°F for the cheesecake layer.

In the bowl of a stand mixer (or with a hand mixer), beat the softened cream cheese and sugar together until completely smooth and creamy, pausing to scrape down the sides of the bowl as needed.

Add the eggs one at a time, mixing well after each addition. Scrape the bowl often to make sure everything is fully incorporated.

Mix in the sour cream and vanilla extract until combined and smooth.

Transfer about half of the cheesecake batter into a separate medium bowl. To that bowl, whisk in the pumpkin puree and pumpkin pie spice until evenly blended.

Spread half of the plain cheesecake batter evenly over the cooled crust.

Drop spoonfuls of the pumpkin batter on top, then use a butter knife to gently swirl the two layers together.

Repeat with the remaining plain cheesecake batter and the rest of the pumpkin batter, swirling again to create a marbled effect.

Bake at 325°F for 35-40 minutes, or until the edges are set and the center has a slight jiggle. The cheesecake will continue to firm up as it cools.

Remove from the oven and let the bars cool completely at room temperature.

Once cooled, transfer the pan to the refrigerator and chill for at least 4 hours, or until the cheesecake is fully set.

Use the parchment overhang to lift the bars out of the pan. Slice into squares or rectangles.

Serve and enjoy.