Preheat oven to 350 degrees F (175 degrees C). Grease and flour three 8 inch round cake pans.
Prepare cake mix according to package directions.
Pour batter into the prepared pans.
Bake at 350 degrees F (175 degrees C) for 30 minutes.
Let cake cool slightly then pierce cakes with a fork.
Pour the coffee liqueur gradually over the three cake layers.
Prepare the chocolate mousse according to the package directions.
Let chill in the refrigerator.
Once cake is cool break it into pieces.
Layer cake pieces, chocolate mousse, crushed butter toffee candy bars, and whipped topping 1/3 at a time in a large glass bowl. Grate the chocolate candy bar over the top.
Let chill in refrigerator for several hours before serving.
