In a medium saucepan over low-medium heat cook together the cocoa powder, hot coffee, and butter. Stir frequently and let cook until all of the butter is melted. Remove from the heat and let cool for ten minutes or so.
Pour liquid ingredients into the dry ingredients & mix together until fully combined, make sure there are no flour streaks left behind but don't over mix the batter or you risk a tough cake.
Pour into the prepared pan and bake for 38-42 minutes, if you stick a knife in the center of the cake it should come out with no wet batter, moist crumbs are okay.