Preheat oven to 350°F. Line a 16 x 9 baking pan with parchment paper and lightly grease it.
In a glass mixing bowl, melt the butter and chocolate over a double boiler until smooth. Remove bowl from heat and stir in sugar. Add the eggs and vanilla and whisk until smooth.
In a separate large mixing bowl, combine cocoa powder, flour, baking powder, and salt.
Pour wet ingredients into dry and fold until just combined. Pour the batter into the prepared baking pan and bake 30 minutes.
While brownies are baking, make the pumpkin pie layer.
Combine all ingredients in a blender and blend until smooth. Alternatively, place all the ingredients in a mixing bowl and beat with an electric mixer until all ingredients are combined and smooth.
After 30 minutes, remove brownie layer from oven and pour pumpkin pie layer over top. Immediately place back in oven and bake another 15 minutes.
Remove brownies from oven and allow to cool completely.
Make the ganache by placing the chopped chocolate in a mixng bowl.
Heat the cream in a small heavy bottom pot. It doesn't have to come to a boil, it just has to be really hot (be careful not to scorch the cream!). Once hot, pour the cream over chopped chocolate. Gently stir until chocolate melts and ganache becomes smooth and velvety. Allow to cool about 15 minutes so that ganache is spreadable.
Pour over cooled brownies and spread to cover.