Preheat the oven to 350F.
Combine the flour, baking powder, and salt in a large mixing bowl.
In a separate bowl, whisk together the melted butter, eggs, brown sugar, and vanilla.
Pour the liquid ingredients into the dry ingredients and mix until well combined.
Remove 3/4 cup of the batter and place in separate bowl.
Add the pumpkin puree, cinnamon, clove, and nutmeg, then stir and set aside.
In the original bowl, add the cocoa powder, milk, and chopped chocolate bar, mixing until smooth.
Pour all but 2 Tablespoons of the chocolate brownie batter into an 8x8” baking pan lined with parchment paper.
Pour the pumpkin batter over the chocolate batter.
Add the remaining chocolate batter and “marble” it over the pumpkin batter.
Bake for 20-25 minutes, or until toothpick comes out clean.