Melt chocolate in a saucepan over low heat until smooth. Set saucepan in hot water to maintain consistency. With small paint brush, brush melted chocolate onto the bottom and up sides of paper candy cups till about 1/8" thick.In a small bowl, combine peanut butter and powdered sugar until smooth. Shape mixture into balls. Put a peanut butter ball in each chocolate coated candy cup. To seal peanut butter balls, spoon another layer of melted chocolate over each ball. Chill or freeze until chocolate has hardened.