In a bowl, combine flours, cocoa powder, yeast, and salt. Stir in molasses, then add beer and 1/2 cup coffee and work the dough with a wooden spoon until the dough pulls away from the sides of the bowl and forms a cohesive ball. You may need an additional 1-2 tbsp coffee to achieve the right texture.
Cover bowl with plastic wrap and a tea towel and set in a warm, draft-free area to rise for at least 12 hours, but preferably closer to 24.
When ready to bake, preheat oven to 450 degrees. After the oven fully heats, set a Dutch oven with the lid on in the oven to heat an additional 15-20 minutes.
While the Dutch oven preheats, flour a work surface and your hands. Turn the ball of dough onto the surface and work into a ball. Cover with plastic wrap and allow to rest as the pot preheats.
When the Dutch oven is done heating, place the dough ball onto a big sheet of parchment and set carefully into the bowl of the pot. Cover with the lid. Bake 30 minutes with the lid on, then remove the lid and bake an additional 8-10 minutes.
Remove bread from the pot and cool on a wire baking rack for at least an hour. After that time, slice and serve!