Heat the oven to 350°F (175°C). Line a 9 x 13-inch metal baking pan with parchment, leaving enough overhang on the long sides to lift out the cooled brownies.

Whisk the melted, slightly cooled butter and sugar together in a large bowl. Add the eggs and vanilla, then whisk until the mixture looks smooth and evenly blended.

In a separate bowl, whisk together the flour, cocoa powder, baking powder, and salt. Fold the dry ingredients into the butter mixture just until no dry streaks remain, then fold in the chocolate chips.

Beat the softened cream cheese and sugar in another bowl until smooth. Beat in the egg, then mix in the pumpkin purée, cinnamon, nutmeg, ginger, salt, and optional vanilla.

Spread approximately half of the brownie batter over the parchment in an even layer. Spread the pumpkin cheesecake mixture over the brownie layer, taking care not to disturb the base.

Drop spoonfuls of the remaining brownie batter over the pumpkin layer. Drag a knife through the batter several times to make a light swirl, but stop before the layers become blended.

Bake for 35–45 minutes, until the brownie edges are set and a toothpick inserted into the chocolate portion comes out with moist crumbs. The pumpkin layer should look set while still having a slight jiggle in the center.

Cool the brownies completely in the pan, then refrigerate them for at least 1 hour, preferably 2–3 hours. Lift them out with the parchment and slice with a sharp knife, wiping the blade between cuts.