In a saucepan over medium heat, combine the confectioners' sugar, butter and heavy cream. Cook, stirring constantly, until smooth. Do not allow the mixture to boil. Remove from heat, and stir in chocolate chips and unsweetened chocolate until melted and smooth. Allow the mixture to cool slightly before using. May be kept in a covered container for a few days at room temperature, or refrigerated for up to 1 week.n
