Mix the quark with sugar, vanilla sugar, egg, oil and milk until smooth. Mix the flour with baking powder and stir in half of it. Add the other half and knead everything into a smooth dough with your hands. Shape into a roll on a floured surface and cut into approx. 12 pieces.
Shape each piece into a ball and roll it out with the corrugated wood, similar to a small pizza. Put 1 teaspoon of Nutella on each top part of the dough and roll the dough into a croissant. Place the croissants on a baking sheet lined with baking paper.
Mix egg yolks with milk and brush the croissants with it. Bake in a preheated oven at 175 degrees for about 20 minutes until golden brown. Take out, let cool down a bit and dust with powdered sugar.