- Soften the mushrooms in water overnight.
- Peel and cube the potatoes, clean and finely chop the bouquet garni and cure the bacon.
- Bring the mushrooms, potatoes, bouquet garni, bacon, caraway seeds and marjoram to a boil in 5 cups of water.
- Bring them to a boil and simmer for 20 minutes.
- Peel the onion and garlic clove, and fry them to golden brown in the butter.
- Sprinkle in the flour and stir to a roux.
- Add the roux to the soup, stirring constantly, and pass the soup through a sieve.
- Season with generous amounts of salt and pepper.
- Combine the egg yolk and the sour cream, remove the soup from the heat, and stir in the egg-cream mixture.
- Garnish with parsley and serve.