For the spinach-cheese dumplings, coarsely chop the spinach, finely chop the onion and fry. Whisk warm milk with egg. Mix spinach, bread cubes, warm egg-milk and let sit.
Add onion, cheese, pepper and salt, mix in flour and form dumplings. Cook the spinach-cheese dumplings in salted water for about 15 minutes and serve as a side dish.