Set oven control to broil. Sprinkle marshmallows over melted chocolate. Broil with top 5 to 6 inches from heat 20 to 30 seconds or until marshmallows are toasted. (Watch closely; marshmallows will brown quickly.) Cool 10 minutes. For bars, cut into 6 rows by 4 rows. Serve warm. Store any remaining bars tightly covered.