Preheat your oven to 350°F (175°C).
In a large bowl, cream together the softened butter and sugar with an electric mixer until smooth.
Beat in the eggs and ½ can of sweetened condensed milk.
Add the flour, cocoa powder, baking soda, and baking powder. Whisk gently until the batter is smooth and no dry streaks remain.
Pour the batter into a 9x13 inch pan and bake for 40 minutes.
Remove from the oven and use the handle of a wooden spoon to poke holes all over the cake.
Slowly pour the caramel sauce and remaining condensed milk over the cake, allowing it to soak in. Let cool for 30 minutes.
Once cooled, spread the Cool Whip evenly over the cake and top with chopped Heath bars.
Slice and serve!