Prepare brownies according to directions on box. While still warm pour Kahlua over prepared brownies - cool.
Prepare chocolate mousse according to directions and crush Heath bars.
Break the brownies into pieces. Arrange half of the brownies in bottom of a trifle bowl. Pour half of the prepared mousse over brownies. Spread 1 (8 ounce) carton of whipped topping over mousse and top with half the crushed Heath bars. Repeat the layers of brownies, mousse, topping and candy bars. Chill until serving time. Serves 15 to 20 people. The brownies may be made a day ahead.
