Bake cake according to directions. Remove cake from oven. While still hot use a wooden spoon to poke holes in cake. Spread milk then fudge over cake. Let cake cool. Then spread cool whip over top. Sprinkle crushed candy bar on top of cool whip. Refrigerate cake. Cake is best if made one day in advance.
Ovens may vary.... so bake according to temps that work for you as in how long you will bake your cake.