Preheat oven to 350°F (175°C). Line an 8×8-inch baking pan with parchment paper.

Melt the butter and chopped semi-sweet chocolate together until smooth. Let cool slightly.

Whisk in granulated sugar and light brown sugar until combined. Mix until glossy and fully incorporated.

Add eggs one at a time, then stir in vanilla extract. Stir just until the batter looks uniform.

Fold in all-purpose flour, unsweetened cocoa powder, and salt just until incorporated. Stop mixing as soon as no dry streaks remain.

Stir in semi-sweet chocolate chips. The batter should be thick and fudgy.

In a separate bowl, beat pumpkin purée, cream cheese, egg yolk, granulated sugar, vanilla extract, pumpkin pie spice, and ground cinnamon until smooth. Scrape the sides as needed for a silky texture.

Spread about two-thirds of the brownie batter into the prepared pan. Press into an even layer.

Spoon the pumpkin mixture evenly over the brownie layer. Use the back of the spoon to level the surface.

Dollop the remaining brownie batter over the pumpkin mixture. Distribute it to cover most of the pumpkin layer.

Use a butter knife to gently swirl the two batters together into a marbled pattern. Avoid overmixing so streaks stay distinct.

Bake at 350°F (175°C) for 35–42 minutes, until the edges are set and the center has a slight jiggle. Look for a crackly top.

Cool completely at room temperature before chilling for at least 1 hour. This helps the marbling set for clean slices.

Cut into 16 bars and serve. Wipe the knife between cuts for sharper edges.