Boil the potatoes, then peel and grate or press them. Melt the margarine a little and add to the potatoes. Work into a dough with flour and baking powder. Season this with salt and pepper.
Roll out the dough about 0.5 cm thick on a work surface and cut out about 20 triangles. Crumble the feta cheese and mix with the chopped parsley. Place a teaspoon of the cheese mixture on the wide side of the triangles, roll up the dough from the wide side and form croissants out of it. Place on a baking tray lined with baking paper. Whisk the egg yolks, brush the croissants with it and sprinkle with sesame seeds.
Bake in a preheated oven at 200 ° C for about 20 minutes.