Bake cake as directed in 13x9 inch pan.
Cool 10 min. in pan, then turn out on wire rack to finish cooling.
While cake is cooling make filling using 1/4 cup LESS milk than is called for in the pudding, and adding 1 teaspoon of rum flavoring.
As soon as cake is cold, get a long piece of thread, twist the ends around your fingers and using thread like a knife cut the cake in half LONGWAYS.
Gently lift the top back into pan, cut side UP.
Spread the filling over and gently put the other half of the cake on top, cut side DOWN.
Spread entire surface with whipped topping, use a spoon to peak it, or swirl it.
Sprinkle ground walnuts around edges only, about 1 or 2 inches wide, leaving center without walnuts.
Remove the candy bar from freezer, peel off the wrapper, and grate the candy over the entire top of the cake.
I usually grate a little over the walnuts as well.