Grease an 8-inch round springform pan (you can use a 7-inch springform pan and get a taller looking cake but you will have to bake longer). Then line with parchment paper on sides and on the bottom.
Preheat oven to 350°F. Beat eggs on highest speed with a stand mixer until about triple in volume, about 6 minutes. The egg consistency is the key to making this recipe work, so don't try to save time on this step. Eggs must be beaten until triple in volume as that is what creates the cake.
Measure out Nutella into a glass bowl. Microwave Nutella for about 20 seconds to make it softer. Add in 1/3 of the egg mixture. Gently stir with a spatula in the same clockwise direction until all of the egg is mixed in and no streaks remain. Then add another 1/3 of egg mixture and fold again until no egg streaks remain. Pour in remaining third and make sure to scrape the foam that sticks to the mixing bowl into the batter and stir until no streaks remain. Make sure to do this in 3 batches because otherwise the whipped eggs may lose too much of the air that has been whipped into them if you try to do it all at once.
Pour batter into springform pan. Bake for 20-25 minutes until knife inserted comes out clean. Let cake cool completely before removing from pan and cutting and serving. , will allow the chocolate flavor to fully develop, otherwise when it is still hot it tastes slightly eggier.