Bake desired flavor of cake according to directions on box in a greased 9x13 pan. When the cake is still hot poke holes in it with a fork and pour caramel topping and sweetened condensed milk over it slowly. Sprinkle half of the crushed butterfingers evenly over cake. When the cake is cool top with cool whip and sprinkle the rest of the butterfingers evenly. Drizzle with reserved caramel. Keep refrigerated.