In a large bowl, blend together the devil's food cake mix, eggs, water, and melted butter until the mixture is smooth and fully combined.

Spray the inside of the slow cooker insert with cooking spray to prevent sticking.

Pour the batter into the slow cooker and smooth it into an even layer.

Cover the slow cooker and cook on high for 2 hours. Do not open the lid during cooking to ensure even rising and baking.

Once the cake is cooked, use the end of a spoon or a skewer to poke holes all over the surface of the cake carefully.

Pour the sweetened condensed milk and ½ cup of caramel topping evenly over the surface of the cake, allowing it to soak into the holes.

Remove the slow cooker insert from the base and let it cool until the bottom is cool to the touch.

Transfer the cake to the refrigerator. Chill for at least 2 hours or overnight for best results.

Once chilled, spread the thawed Cool Whip evenly over the top of the cake.

Sprinkle the chopped Heath bars generously over the whipped topping.

Drizzle with caramel and chocolate sauce over the top for extra sweetness and decoration.

Serve the cake by scooping out portions with a large spoon.