Preheat your oven to 350°F (175°C). Grease and line an 8x8-inch baking pan with parchment paper.
Make the brownie batter: In a large bowl, whisk together melted butter, granulated sugar, eggs, and vanilla until glossy. Stir in cocoa powder, flour, and salt until just combined.
Make the pumpkin batter: In a separate bowl, whisk together pumpkin puree, egg, brown sugar, spices, salt, and flour until smooth.
Pour about 2/3 of the brownie batter into the prepared pan. Smooth into an even layer.
Gently spoon pumpkin batter on top. Add remaining brownie batter in dollops.
Use a butter knife to swirl the batters together in a marbled pattern. Don’t overmix!
Bake for 30–34 minutes, or until a toothpick inserted comes out with a few moist crumbs.
Cool completely before slicing (if you can wait!).