Prepare and bake the chocolate cake mix according to the package instructions, usually in a 350°F (175°C) oven for around 25–30 minutes. Let cool.

Once cooled, poke holes evenly across the top with a wooden spoon to allow hot fudge to seep in.

Warm hot fudge in the microwave until pourable, then pour it over the cake, allowing it to seep into the holes.

Whisk chocolate pudding mix and cold milk together in a mixing bowl until thickened, then pour over the hot fudge layer.

Cover and refrigerate for about 20 minutes to allow pudding to set.

While the first pudding layer sets, mix the second package of chocolate pudding with remaining milk and whisk until thick.

Fold in the thawed Cool Whip and about ¾ of the crushed Oreos to form the topping mixture.

Spread the Cool Whip and Oreo mixture evenly over the set pudding layer on the cake.

Sprinkle remaining crushed Oreos over the top as garnish, then serve or refrigerate until ready.