1. Preheat oven to 350 degrees F. Prepare brownie mix as directed on package. Spread in greased foil-lined 15x10x1-inch baking pan.
2. Bake 15 minutes or until toothpick inserted into center comes out almost clean. Cool in pan on wire rack.
3. Meanwhile, beat confectioners' sugar, 7 tablespoons of the butter, cream and peppermint extract in large bowl with electric mixer on medium speed until well blended and smooth. Spread evenly over cooled brownie. Refrigerate 30 minutes.
4. Microwave chocolate and remaining 8 tablespoons (1 stick) butter in large microwave bowl on HIGH 2 minutes or until butter is melted. Stir until chocolate is completely melted. Spread over top of chilled brownie. Sprinkle with crushed peppermint candies, if desired. Cut into bars.