Preheat oven to 350 degrees F. Line a 9x9 baking pan with foil or parchment paper. Spray the bottom of the lined pan with non-stick oil.
Melt butter and chocolate in a heavy pot on low heat, stirring until smooth and melted. Remove from heat and set aside.
Combine sugar and eggs with an electric mixer and beat until very well combined. Add flour, baking powder, and salt, and stir until combined, but do not overmix.
Divide the egg, sugar, and flour mixture evenly into two bowls. To one bowl, add the melted chocolate mixture and stir until combined. In the other bowl, add pumpkin, oil, and spices to the mixture and stir until combined.
Layer pumpkin and brownie batters into the 9x9 pan, and use a knife to swirl the batters together. If adding chocolate chips to the top, sprinkle them on top of the batter. Bake for approximately 40-45 minutes or until a toothpick inserted into the center comes out almost clean. Allow to cool on a wire rack prior to serving.
Notes
Chef Jenn's Tips
For a beautiful swirl pattern, gently drag a knife through the batter in a figure-eight motion.
Use semisweet or bittersweet chocolate for the best contrast between the chocolate and pumpkin layers.
Make sure your eggs are at room temperature before mixing; this helps everything combine more smoothly.
Don’t overmix the batter once you add the flour; this ensures your brownies remain fudgy and tender.
If you want a stronger pumpkin flavor, you can lightly increase the pumpkin pie spice, but stick to the listed amount for the perfect balance.