Zurek sour rye soup

Method

1. For the homemade sour rye liquid, put the flour, water, bay leaves and allspice berries in a jar and cover the jar with muslin (it needs access to the air to ferment). Leave in a warm place for 2 days, stirring carefully twice a day. After 2 days, add the garlic. If any sediment forms on the top – which is harmless – scrape it off. Once fermented (it should look a bit bubbly and smell slightly sour), strain it and reserve the liquid.
2. For the soup, rinse the dried porcini of dust, put into a small bowl, pour over the boiling water and set aside to soak.
3. Heat 50 ml of the olive oil in a large, heavy-bottomed saucepan, add the shallots and fry until soft, then add the garlic, potatoes, celery, bay leaves, allspice berries, marjoram or oregano, thyme, peppercorns and 1 tablespoon salt. Fry for a few minutes until the potatoes start to colour, then add the sour liquid and the soaked porcini with their soaking liquid.
4. Bring to the boil, then turn down the heat and simmer for 15–20 minutes until the potatoes are tender and the mushrooms soft. Check the seasoning, adding salt, if needed, and white pepper to taste. If you’d like the soup more liquid, you could add 500 ml vegetable or mushroom stock at this stage. Grate in some fresh horseradish and cook for another 20 minutes or so. Remove the bay leaves if you wish. Fry up the fresh mushrooms for the garnish with the garlic in the remaining 25 ml olive oil, then serve the soup topped with the fried mushrooms and dill.