Bake cake the day before according to package directions. When cool, prick with a fork and drizzle Kahlua or coffee over it.
Prepare mousse according to package directions and chill.
To assemble: Cut up cake into bite sized pieces. Break candy with hammer right in package. Layer as in trifle: cake, mousse, candy bits, whipped cream. Repeat to fill a large glass bowl. Chill. Serves 10-12.