Mix the flour with baking powder and cornstarch and then sieve. Beat the eggs with sugar and vanilla sugar with a hand mixer for 3-5 minutes until frothy, then add oil and eggnog and continue beating. Then stir in the flour mixture loosely, now stop beating!
Put 2/3 of the dough in a buttered and floured bundt cake pan. Stir the Nutella into the remaining third. Place the dark dough on the light dough and marble with a fork or chopstick.