Preheat your oven and prepare the yellow cake mix according to the package directions for a 9-inch x 13-inch baking dish.
While the cake is baking, mix together caramel sauce and sweetened condensed milk in a medium bowl.
Take the cake out of the oven. While it's still warm poke holes all over the top with the back of a wooden spoon, skewer, or a fork.
Pour the caramel mixture all over the warm cake and then let it sit on a wire rack until completely cooled. (The cake will soak up the caramel)
Crush up all the Butterfingers and sprinkle 2 of the candy bars evenly over the cake.*Pro Tip: Put the candy bars in the freezer so they'll crush better. Then crush the Butterfingers in the wrappers, cut the tops off, and pour them out over the cake.
Frost the cake with the Cool Whip so the entire top is covered.
Sprinkled the top fo the cake with the remaining 2 crushed Butterfingers. Store in the fridge until ready to cut into 12 slices and serve.