Heat the oil and sweat the onion and garlic until translucent. Add the cabbage, carrot and celeriac and sweat all together.
When the vegetables have softened slightly add the stock and the bay leaves and simmer over a medium heat for about 15 minutes. Season the soup with salt and pepper and add marjoram to taste.
Clean and slice the ceps. Heat the butter in a frying pan and briefly toss the ceps. Add to the soup shortly before serving.
Season the sour cream to taste with lemon juice, salt and pepper.
Wash the sorrel, pat dry and cut into thin strips. Place on top of the sour cream and hand separately with the soup.