Simmer the leg slice with celery in 2 liters of water for 45 minutes until a strong broth is formed. Salt, pepper. Then take out the celery, throw it away and cut the meat into small pieces, put back in the broth.
Peel the potatoes, cut into large cubes and add to the broth with the bay leaf. Cook for another 10 minutes. In the meantime, chop the onion and fry in a little oil until golden. Peel the carrot, add to the onions and fry lightly. Add the spaetzle with vegetables to the soup and then cook for another 12 minutes.
Arrange the soup in a plate with parsley and a teaspoon of sour cream to taste.