Preheat oven and prepare the chocolate cake mix as directed on the box, using 1 cup of milk, 3 eggs, and 1/2 cup vegetable oil. Bake in a 9×13-inch pan.

Once baked, let the cake cool for about 10 minutes. Use the handle of a wooden spoon to poke holes all over the surface.

In a large bowl, whisk together 3 cups cold milk, 4 packets hot cocoa mix, and 2 boxes of instant chocolate pudding until smooth.

Immediately pour the pudding mixture evenly over the warm cake, letting it seep into the holes.

Refrigerate for at least 2 hours or until pudding is fully set.

Spread the whipped topping evenly over the chilled cake.

Sprinkle mini marshmallows on top and drizzle with chocolate syrup if desired.

Slice and serve chilled or slightly softened at room temperature.