Preheat oven to 350°F (175°C). Line an 8x8-inch metal baking pan with parchment paper, leaving an overhang on the sides for easy lifting. In a heat-safe bowl set over a pot of barely simmering water, melt the butter and chopped dark chocolate together until glossy and smooth. Remove from heat and let cool for 5 minutes.

Whisk granulated sugar and brown sugar into the warm melted chocolate mixture. Whisk in the eggs one at a time, beating vigorously for 1 to 2 minutes until glossy (this creates the shiny crackly top). Whisk in vanilla extract. Gently fold in flour, cocoa powder, and sea salt with a rubber spatula just until combined—do not overmix.

In a separate medium bowl, beat the softened cream cheese, pumpkin puree, sugar, egg yolk, cinnamon, nutmeg, and ginger with a hand mixer or whisk until smooth, velvety, and completely lump-free.

Spread about 3/4 of the fudgy brownie batter into the prepared baking pan. Dollop the pumpkin cheesecake mixture across the surface in large spoonfuls, then dollop the remaining brownie batter in the spaces between. Use the tip of a butter knife or skewer to gently drag figure-eight swirls across the top to create a gorgeous marbled pattern.

Bake at 350°F (175°C) for 30 to 34 minutes. A toothpick inserted into the center should emerge with moist crumbs attached, not wet batter. The cheesecake swirl will be gently set with a slight golden edge.

Let brownies cool completely in the pan on a wire rack for at least 1 hour, then chill in the refrigerator for 1 hour for clean, razor-sharp bakery slices. Lift out using the parchment overhang and cut into 16 decadent squares.