Preheat oven according to brownie directions. Bake brownies according to package directions; let cool. Meanwhile, prepare chocolate mousse according to package directions. Break candy bars into small pieces in food processor or by gently tapping the wrapped bars with a hammer. Break up half the brownies into small pieces and place in the bottom of a large glass bowl or trifle dish. Cover with half the mousse, then half the candy and then half the whipped topping. Repeat layers with the remaining ingredients. Yield: Feeds up to 24 (or 1 serious chocoholic!).