Place 2 ounces semisweet chocolate pieces, coarsely chopped, in small metal bowl and place over saucepan of simmering water. Stir chocolate until smooth. (Or melt chocolate in microwave-safe bowl, uncovered, in microwave oven on high power for 50 to 60 seconds.) Spoon melted chocolate into plastic food-storage bag; press out all the air and seal. Cut off very small piece from one corner to make about 1/16-inch hole. Starting in center of each cupcake, draw spiral with chocolate. Using tip of paring knife or wooden pick, draw 6 to 8 lines from middle of each cupcake to edge, making cobweb pattern.