Melt the dark chocolate by breaking up into small pieces in a bowl and heating for 30 second intervals in a microwave, stirring in between. Set aside to cool whilst making the brownies.
In a large bowl or the bowl of a stand mixer combine the melted butter, and both the brown and granulated sugars on a medium speed until totally combined. Add the eggs and vanilla and mix again. Add in the melted chocolate.
Fold in the flour and cocoa powder.
In the pan, pour in half the brownie mixture, followed by half the funfetti batter. Top with the remaining brownie mix, then the funfetti cake batter. Bake for 40-45 minutes until a skewer inserted comes out clean. If it is browning on top too much, cover with foil and return to the oven for an additional 5-10 minutes.