The chocolate flavor of this dough comes from cocoa powder, so the quality of cocoa you use will bear greatly on the results. Buy the best Dutch-processed cocoa powder you can find, preferably an imported brand such as Valrhona or Droste. The method used here is the same as for the Standard Tart Dough, but the baking presents an additional challenge. As the tart is a deep shade of cocoa, color won’t help much to determine when it’s finished. Engage your senses of smell and touch: A rich chocolate aroma and a dry interior mean the tart shells are done. If the tarts are close to being finished but you’re not sure, pull them from the oven. It’s fine to put them back in the oven if they do need additional time.