Preheat the open to 350°F and grease a deep dish pie pan.
Brownie Batter:
Heat the chocolate chips, brown sugar and butter in a medium saucepan over medium-low heat. Stir occasionally until just melted and combined.
Remove from heat and let sit for a minute. Whisk in 2 eggs, one at a time, then the vanilla. Add the cocoa powder, baking powder, flour and salt, whisking until just combined.
Pour about a third of the batter into the pie pan and bake 20 minutes. Set aside the rest of the batter for later.
Pumpkin batter:
Combine heavy cream, sugar, pumpkin puree, pumpkin pie spice and remaining egg & flour in a mixing bowl. Stir until smooth.
Pour the pumpkin batter over the cooked brownie batter.
Stir a tablespoon of water into the remaining brownie batter, then use a spoon to scoop it into the pumpkin batter, swirling as you go.