Preheat oven to 350 degrees F and spray a 9x13-inch baking dish with cooking spray.
Mix and bake cake according to box directions.
Let cool 10 minutes and then poke holes in it with the back of a wooden spoon.
Combine caramel sauce, peanut butter and sweetened condensed milk in a large glass measuring cup. Microwave for 30 seconds and then stir until smooth.Pour mixture overcake, letting it seep into holes.
Cover cake with plastic wrap and refrigerate for at least 2 hours.
Spread Cool Whip on top and sprinkle with crushed butterfinger candies.