Preheat oven to 350°F and lightly spray one 9×13 inch OR two 8×8 inch pans with non-stick spray.
In a heavy bottomed sauce pan, double boiler, or microwave, melt the butter and unsweetened chocolate together until just melted. Set aside to cool slightly.
In a large bowl, add the melted butter and chocolate, and whisk until combined.
Add the sugars and vanilla and whisk vigorously until all of the sugar is combined.
Add the eggs, one at a time, whisking to make sure the whole egg is evenly incorporated before adding the next.
Sift the cocoa powder into the mixture using a sift or a fine mesh sieve. (You can skip sifting it, however it helps to relieve your brownies of cocoa clumps which are very unpleasant to bite into.
In a separate, medium sized bowl, add the flour and the salt. Mix them thoroughly.
Add the flour to the rest of the ingredients. The mixture will be very thick and you might have to switch from a whisk to a spatula to finish incorporating the flour.
For the Pumpkin Cheesecake Batter:
In a medium-sized bowl, using a hand mixer, beat the cream cheese until light and fluffy, 1-2 minutes. Add the pumpkin and mix until homogeneous. Add the egg, sugar, and spices. Beat for 3-4 minutes until light and fully mixed. Now you are ready to assemble your brownies!
Reserve 1/2 cup of brownie batter and set it to the side. Pour the remaining brownie batter into prepared pan. Pour the pumpkin cheesecake batter on top of the brownie batter. Using a spoon dollop the reserved ½ cup of brownie batter on top of the pumpkin cheesecake layer in little blobs. When you have used it all, take a knife and swirl the batters together to give it the cool look. Bake in preheated oven for 25-35 minutes.
Once cooked, allow to cool for 15 minutes before cutting and eating. I like to keep mine in the fridge, they're so good cold!