Preheat the oven to 350°F (175°C)
Lightly coat a 9x13-inch baking pan with non-stick cooking spray, set aside
mix cake according to the box directions
Pour the prepared cake batter into the pan and bake according to the package directions for a 9x13-inch cake
Check doneness by inserting a toothpick into the center; if it comes out clean, remove the cake from the oven
Use the end of a wooden spoon or a chopstick to poke holes all over the cake, about ½ inch apart
Pour the sweetened condensed milk over the hot cake, allowing it to soak into the holes
Pour the caramel sauce over the cake, ensuring even coverage
Set the cake aside to cool completely to room temperature
Once cooled, spread the Cool Whip evenly over the cake
Sprinkle Heath Bar bits generously over the top (use half the bag or more to preference)
Slice and serve immediately