Instructions

1. 1
   Boil potatoes with their skins, then peel them, chop onto small pieces and roast it in a pan (without adding grease).
2. 2
   Put 250 ml tepid water into a bowl. Stir in the sourdough starter. Cover with a clean cloth, and let rest at room temperature for 30 minutes to 3 hours.
3. 3
   Put 1000 ml water into a stockpot. Add the dried mushrooms and caraway, and boil for at least 15 minutes to make a strong broth.
4. 4
   Carefully add the sourdough mixture into the broth, stirring well—there is a danger that the sourdough will shrink into small dumplings.
5. 5
   Boil the soup, stirring, until the sourdough thickens the mixture. This should take about 10 minutes.
6. 6
   Sauté the chopped onion with butter in a pan. Stir it into the soup.
7. 7
   Beat the eggs with a pinch of salt, and scramble them in an ungreased pan. Stir the cooked eggs into the soup.
8. 8
   Season the soup to taste with salt and vinegar. It should be mildly sour, flavored primarily by the mushrooms and sourdough.
9. 9
   Served the soup hot, garnished with the chopped herbs, with the potatoes as a side dish. Individual diners may wish to add additional vinegar and salt to taste.