Preheat the oven to 325 degrees. Beat the grated chocolate, sugar, and egg yolks in a bowl until thick and creamy. Fold in the stiffly beaten egg whites. Sift the flour over the mixture and fold it in gently. Set cupcake papers out on a cookie sheet and spoon a small amount of batter -- not more than 1/4 cup -- into each one. Sift the confectioners' sugar over the batter. Bake immediately, until the tops are firm, about 15 to 20 minutes. Remove from oven and cool on a wire rack.
Recipe adapted from Traite historique et pratique de la cuisine, printed in 1758