Spray a 9" cheesecake pan with cooking spray and then line it completely with parchment paper. The cooking spray will help the paper adhere to the pan. Cover the bottom and the sides, because the cake it very sticky.
Put the eggs in the bowl of a stand mixer fitted with the whisk attachment. Beat on medium for 2 minutes, then turn to high for 8 minutes, until the eggs have tripled in volume. The bowl of the stand mixer will almost overflow! (Don't worry, they will lose much of their volume as they get folded into the Nutella)
Meanwhile, microwave the Nutella for just 20-25 seconds so it softens a bit.
In your largest mixing bowl, fold 1/3 of the eggs into the Nutella. Use a rubber spatula and turn the bowl with one hand while you gently fold with the other. This process will be messy and you will think the whole thing has gone terribly wrong, but keep at it. When the eggs have been completely incorporated, fold in the next third, and again until all the eggs are mixed in. Do this gently so you keep as much of the loft of the eggs as possible.
Bake for 25-35 minutes, until the center is just set. Don't over bake, and watch it carefully towards the end.
Cool completely before attempting to open the pan and remove the cake.
Sprinkle generously with cocoa powder or confectioner's sugar, and garnish with whatever you like.