Add all ingredients for the pumpkin swirl to a bowl and stir well to combine. Set aside.
For the brownies:
Melt butter in the microwave and then set aside to cool.
Sift dry ingredients together in a bowl; flour, sugar cocoa powder, baking powder and salt.
In another small bowl whisk together the eggs and vanilla. Add mixture to the dry ingredients and gently stir.
Pour melted and (slight cooled butter) over the top and mix just until combined (don't overmix).
Pour 3/4 of the brownie batter into the bottom of a greased 8x8'' pan and smooth into an even layer.
Pour the pumpkin mixture on top and smooth into an even layer.
Spoon remaining brownie batter over the top. Use a butter knife to gently swirl the batter in both directions.
Bake at 350 degrees F for 25- 33 minutes or until the brownies are set and a toothpick inserted into the center comes out clean (or with just a few crumbs). Allow to cool for at least 15 minutes before cutting.