Preheat oven to 350°F.
Combine cake mix and dry pudding mix with eggs, vanilla, milk, canola oil and sour cream.
Beat on medium speed until well combined, about 2 minutes.
Pour batter into 9x13" baking dish and bake for 20-22 minutes or until toothpick inserted into the middle of the cake comes out clean.
Allow to cool for 10 minutes.
While the cake is still warm, use the end of a wooden spoon to poke holes all over the top of the cake being careful not to go all the way to the bottom.
Heat the hot fudge sauce in the microwave on full power for 30 seconds to thin it out; if you need more time, continue at 15 second increments until thin.
Pour the entire jar of hot fudge sauce over the cake and allow it to soak into the holes.
Let stand until completely cooled.
When the cake has cooled, prepare the pudding layer by mixing a package of instant chocolate fudge pudding with 2 cups of cold milk.
Immediately pour the pudding mixture over top of the cake and spread into an even layer.
Place cake in the fridge for at least 15 minutes.
Meanwhile, in a bowl combine the whipped topping and hot cocoa mix. Stir until combined.
Spread whipped topping over top of cake.
Sprinkle chopped chocolate on top.