Prep the pan and oven: Preheat the oven to 350°F (175°C). Line an 8-inch square pan with parchment, leaving overhang for easy lifting. Lightly grease the paper.

Melt chocolate and butter: In a heatproof bowl, melt butter and chocolate together in the microwave in 20–30 second bursts, stirring between each, until smooth. Cool 5 minutes.

Mix sugars and eggs: Whisk granulated sugar, brown sugar, eggs, and vanilla into the melted chocolate until glossy and thick.

Add dry ingredients: Sift in flour, cocoa powder, and salt. Fold gently with a spatula until just combined. Do not overmix. Set aside.

Make the pumpkin cheesecake mixture: In a separate bowl, beat cream cheese until smooth. Add pumpkin puree, sugar, egg yolk, vanilla, pumpkin spice, flour, and a pinch of salt. Mix until creamy with no lumps.

Layer and swirl: Spread about 2/3 of the brownie batter into the prepared pan. Dollop spoonfuls of the pumpkin mixture over the top, then add the remaining brownie batter in small scoops. Use a butter knife to gently swirl, pulling through the layers in figure-eights. Aim for 3–4 passes so you keep distinct ribbons.

Bake: Bake 32–38 minutes, until the edges are set and the center looks slightly glossy but not jiggly. A toothpick should come out with a few moist crumbs, not wet batter.

Cool completely: Set the pan on a rack and cool to room temperature. For the cleanest slices and best texture, chill at least 2 hours before cutting.

Finish and serve: Lift out with parchment, slice into squares, and, if you like, sprinkle a little flaky sea salt on top for contrast.