Preheat the oven to 325°F / 165°C and prepare a 9-inch square baking pan by spraying it with baking spray. Place a piece of parchment paper in the bottom of the pan after spraying. Set the pan aside.
In a small pot, combine the butter and 1 cup of chocolate chips. Melt over low heat and stir constantly until the butter and chocolate have melted together. Remove the pan from the heat and set aside.
Add the sugar, brown sugar, eggs, and whisk until well mixed in a medium mixing bowl and whisk well to combine.
In another medium bowl, mix the flour, baking powder, and salt, then slowly incorporate into the egg mixture and stir well, ensuring there are no lumps.
Divide the flour and egg mixture into two separate bowls.
Add the melted butter and chocolate to one bowl and stir well.
Add the pumpkin puree, oil, and spices to the other bowl and stir to combine. Add the remaining chocolate chips to this bowl and fold them in.
Pour the melted chocolate batter into the prepared pan and pour the pumpkin batter on top, layering the batters. Use a knife to swirl them together gently.
Bake the brownies for 40 minutes until the batter is set. Let the brownies cool in the pan before slicing and serving.