Prepare cake based on package instructions and bake in a 9×13 pan.
After removing cake from oven, immediately poke several holes all over the top with a fork. Mix sweetened condensed milk and caramel together, pour over hot cake, spread it over the entire cake.
Cover and refrigerate until chilled.
After cake has chilled completely, spread cool whip over the top and sprinkle crushed Butterfinger bar on top of cool whip.
