Heat oven to 350°F. Line an 8-inch square pan with parchment and lightly grease.
Whisk melted butter, granulated sugar, and brown sugar until glossy.
Beat in eggs and vanilla until smooth and slightly thickened.
Combine flour, cocoa, baking powder, and salt in a bowl. Whisk to break up any lumps.
Fold dry ingredients into the wet mixture just until no dry spots remain. Stir in chocolate chips, if using.
Beat cream cheese until smooth. Mix in pumpkin puree, sugar, egg yolk, pumpkin pie spice, cinnamon, vanilla, and a pinch of salt until creamy.
Spread about two-thirds of the brownie batter in the pan. Dollop spoonfuls of pumpkin mixture over the top, then add the remaining brownie batter in small mounds.
Drag a butter knife through the layers to create swirls. Bake 30–34 minutes, until edges are set and the center looks slightly fudgy.
Cool completely in the pan on a rack. Lift out, slice into squares, and serve.