Make a smooth dough from soft butter, quark, flour and baking powder. Place in the refrigerator for 1- 1 1/2 hours. You can also make the dough the day before.
Roll out very thinly into a rectangle on a floured surface and then brush with the cream cheese. Cut the dough into oblong triangles. Place a small piece of salmon on the wide piece, roll it up from the broad side and bend it into croissants. Place the croissants on a parchment-lined baking sheet. Brush with egg yolk milk.
Bake at 180 degrees for 20-25 minutes. They should be beautifully golden brown.
The croissants taste great even without salmon.
I always do both variants and roll them up differently. I just cut the ones without salmon into strips and roll them up. Then you can tell them apart more easily.