Grease a springform pan. Don't be shy with the shortening or whatever you use, because this cake WILL stick if you're not careful.
In a mixing bowl, beat the eggs until they are triple in volume. Use the highest speed and plan on mixing at least 8-10 minutes. (If you don't get the consistency and volume right, you're going to have some issues so it's important to follow this and not try to shorten the time. This is truly the step that will make the cake, so skipping it = disaster! )
Weigh the Nutella on a digital kitchen scale. Microwave the Nutella about 20 seconds or so to soften the Nutella a bit.
Gently mix together the Nutella and 1/3 of the egg mixture with a spatula until egg is well combined and there are no streaks.
Add in another 1/3 of the egg mixture and repeat; folding again until there are no egg streaks.
Repeat one last time with the last of the egg mixture using the spatula to scrape the foam that is still in the bowl into the batter. Stir again until no streaks remain. (The gentle and slow combining of the ingredients are how this cake bakes up fluffy, so don't try to skip any of these steps or do them differently.
Pour your batter into your prepared springfoam pan. Bake at 350 degrees F for 20-25 minutes or until a toothpick inserted in the center comes out clean.
Allow the cake to cool completely to room temperature before you remove it from the springform pan. This cake should not be served hot, it needs to cool completely before cutting and serving.