Preheat the oven to 350°F (175°C) and line an 8x8 inch baking dish with parchment paper, leaving an overhang for easy removal.

Whisk the flour, baking powder, and salt in a medium bowl until combined.

In another bowl, whisk the melted butter and sugar until smooth. Add eggs one at a time, whisking after each, then stir in the vanilla.

Divide the mixture into two bowls. Stir cocoa powder and chocolate chips into one and pumpkin purée with pumpkin pie spice into the other.

Spread the chocolate batter evenly in the pan, then gently spread the pumpkin batter on top. Swirl with a knife or skewer for a marbled look if desired.

Bake for 25–30 minutes until a toothpick inserted in the center comes out with a few moist crumbs. Cool completely in the pan.

Lift the brownies out using the parchment, cut into squares, pipe green frosting for vines, and top with mini pumpkin candies to create a “pumpkin patch.”