Ingredients
For the Cake:
1 pkg. (15.25 oz.) dark chocolate cake mix

Ingredients listed on the box to make the cake
1 box (3.56 oz.) instant Hershey’s Special Dark Chocolate Pudding mix
4 cups milk, divided
1 jar (12.8 oz.) Hershey’s Special Dark Chocolate topping
For the topping:
1 box (3.56 oz.) instant Hershey’s Special Dark Chocolate Pudding mix
1 container (8 oz.) frozen whipped topping, thawed
1 Giant (6.8 oz.) Hershey Dark Chocolate candy bar, chopped

Instructions
Bake the cake according to package directions using a 9×13-in. baking pan.
Mix the pudding mix with 2 cups of milk in a medium bowl. Poke holes in the hot cake with the round end of a wooden spoon and slowly pour this mixture over the cake, trying to fill the holes.
Microwave the chocolate topping (with the lid off) for about 45 seconds or until it pours easily. Pour evenly over the top of the cake. Let the cake cool completely.
In a medium bowl, combine the second pudding mix with the additional 2 cups of milk. Carefully fold in the whipped topping. Spread the mixture evenly over the top of the cake. Sprinkle the chopped candy bar over the top.
Refrigerate for at least 4 hours. Store the cake (covered) in the refrigerator.
Notes
If you cannot find the Hershey’s Special Dark Chocolate Pudding at your local store – you may substitute any instant chocolate pudding in its place.
I found the chocolate topping near the ice cream toppings at my local big box store.