I make this same cake but a little different.
I use a devil's food chocolate cake
1 can of condensed sweetened milk
1 jar of butterscotch caramel ice cream topping
1 tub of cool whip
1 package of Heath toffee pieces
I bake the cake as directed. Once cooled poke holes in top and pour the condensed milk and ice cream topping all in the holes.
Cool then top with cool whip and crushed heath toffee pieces.
It is awesome too. The milk really makes it super moist.