In a saucepan, melt the two chocolates with the butter. Cool slightly. In a large bowl, mix the flour and sugar. Whisk the eggs into the dry ingredients. Pour the chocolate into the egg mixture and stir until well blended; chill at least 3 hours. Heat the oven to 350°F. Line a muffin tin with muffin papers. Scoop about 1/2 cup batter into each tin so that the curve of the batter is even with the rim of the cup (refrigerate extra batter in an airtight container for up to a week). Bake the muffins until the tops puff and crackle and are slightly soft to the touch, and a toothpick stuck in the center has moist but not wet crumbs clinging to it, about 30 minutes.
nutrition information (per serving):
Photo: Ben Fink