Chocolate Truffle Filling

Microwave semisweet chocolate squares and 6 tablespoons butter in a large microwave-safe bowl at HIGH 1 1/2 to 2 minutes or until melted and smooth, stirring every 30 seconds. Stir in 1/4 cup whipping cream. Stir in 2 1/2 cups powdered sugar, adding remaining 1/4 cup whipping cream, 1 tablespoon at a time, if necessary, until mixture is smooth and creamy. Let mixture cool completely.