This recipe is one part of a master brownie recipe Medrich designed to use whatever chocolate you have in the house — but the best version happens to be the one that only requires cocoa powder. By taking out the chocolate, with its inevitable fat and almost-inevitable sugar, Medrich was able to control and fine-tune the proportions of both. When she added back in the fat (via butter), the middles stayed softer. When she added back in granulated sugar, the crusts were shinier and more candy-like. Any cocoa will work, but natural (not Dutch process) will taste more richly of chocolate.