Preheat the oven to 180 ° C. Grease the soufflé molds well and place on a tray.
Peel the potatoes, cut in half, cook in salted water for about 25 minutes and drain. Cut about 200 g of the potatoes into small cubes, press the remaining ones through a potato press, spread them out on a board and let them evaporate.
Melt the herb butter in a pan. Peel the onions, dice finely and sauté until translucent.
In the meantime, finely dice the feta cheese.
In a bowl, mix the onions with the feta cheese, quark, parmesan, egg yolks, spices and the mashed potatoes well.
Beat the egg whites until firm. Pull the potato cubes and the egg whites into the rest of the mixture. Season the mixture vigorously and pour it into the molds. Bake the souffles until golden brown in approx. 15 minutes. Loosen the edge with a knife, turn the souffles out of the molds and serve.