Preheat oven to 350 degrees F. Liberally grease a 13x9" rectangular baking pan with cooking spray; set aside.

In a large bowl, prepare the cake batter according to package directions. Stir in the dry instant pudding mix to combine. Pour the batter into the prepared baking pan and bake for approx. 23-27 minutes or until a toothpick inserted near the center comes out clean or with moist, not wet, crumbs. Cool for about 20 minutes.

Using the handle of a wooden spoon or a skewer, poke holes all over the surface of the cake. Drizzle on 3/4 of the jar of caramel sauce and the entire can of the sweetened condensed milk. It may seem like a lot, but the cake absorbs a lot of this. Cover the cake with plastic wrap and refrigerate for at least 6-8 hours, preferably overnight.

An hour before serving, spread on the Cool Whip in an even layer and sprinkle on the toffee bits. Drizzle with the leftover remaining 1/4 jar of caramel. Refrigerate uncovered for an hour to set, before cutting into squares to serve.