Bake cake mix according to directions on box in a 9x13 greased pan. When the cake is still hot poke holes in it with a fork or the end of a small wooden spoon. Pour caramel topping and sweetened condensed milk over it slowly. Put half of the butterfingers evenly on top of cake. When the cake is cool frost with cool whip and sprinkle with the rest of the crushed butterfingers. Drizzle with reserved caramel and refrigerate until ready to serve.