Preheat the oven to 350°F. Line an 8x8-inch baking pan with parchment paper, leaving overhang on the sides.

Melt the butter and chopped semisweet chocolate together until smooth and glossy. Let cool slightly.

Whisk the granulated sugar and brown sugar into the chocolate mixture. Add the eggs and vanilla extract and whisk until smooth.

Fold in the flour, cocoa powder, and salt just until combined. Reserve about 1/4 cup of the brownie batter for swirling.

Spread the remaining brownie batter evenly into the prepared pan.

In a separate bowl, beat the softened cream cheese until smooth.

Add the pumpkin puree, sugar, egg yolk, vanilla extract, and pumpkin pie spice. Mix until creamy and fully combined.

Spread the pumpkin cheesecake mixture evenly over the brownie batter in the pan.

Dollop the reserved brownie batter over the pumpkin layer and use a butter knife or skewer to create swirls.

Bake for 35 to 40 minutes, until the edges are set and the center has a slight jiggle. A toothpick inserted into a brownie section should come out with moist crumbs.

Cool completely at room temperature, then refrigerate for at least 2 hours before slicing into 16 brownies.