Mix the sugar with the milk, oil, quark and a pinch of salt. Mix the flour with the baking powder and sieve over it, add the chopped chocolate and knead into a smooth dough. (Kneading hook of the hand mixer) Let the dough rest in the refrigerator for about 15 minutes.
Roll out the dough on a floured surface into a rectangle (40 x 20 cm) and cut into 6 rectangles. These then again diagonally in triangles. Roll up each triangle well from the narrow side to the tip (not loosely, rather tight) and bend into croissants.
Place the croissants on a parchment-lined baking sheet. Mix the egg yolks with a little water and brush the croissants with it.
Bake in the preheated oven at 180 ° C (top / bottom heat) on the middle rack for about 20-25 minutes until golden brown.
Let it cool down and dust with powdered sugar if you like.