Knead the dough ingredients into a pliable, not too firm dough. Cover and let rest for 1 hour. Wash the spinach thoroughly, cook in salted water, drain, and squeeze out excess water. Mix with parsley and puree the mixture. Sauté the finely chopped onion in butter briefly, sprinkle with flour, then add hot milk, stir well, and let thicken slightly. Add the pureed spinach and season with salt, pepper, nutmeg, and Parmesan. You can also add some quark. Let the filling cool. Roll out the dough very thinly and work quickly to prevent it from drying. Use a round cutter or a glass to cut discs, place a small spoonful of filling in the center, dust hands with flour, fold over, and press the edges together immediately. Poach the Schlutzkrapfen in salted water, drain, and serve with grated Parmesan and melted butter.