Polish sour rye soup (Zurek Polski) This soup is made from sour rye flour (fermented) like sourdough For the kwas 75 g wholemeal rye flour 600 ml boiled, cooled water 1/4 clove garlic For the soup 1 1/4 liters vegetable stock (or beef/chicken bones) 100 g bacon 100 g onions 1 can mushroom 400 ml kwas 300 ml sour cream 5 medium potatoes, cooked and diced 100 g smoked sausage, diced Rinse out an earthenware jar or any non-aluminium container with boiling water. Put the flour in the jar and mix to a liquid paste with a little of water. Leave the mixture to settle for a few minutes, and then pour on the remaining boiled water. Chop the garlic and add. Cover the top of the jar with muslin or pierced cling film and leave in a warm place for 4 to 5 days to ferment. Strain and use as required. If stored in an airtight container, it will keep for a few weeks. Heat the stock. Chop bacon and onion and add to stock. Simmer for 10 minutes. Add mushrooms, kwas, cream and garlic. Season with salt and pepper. Allow to simmer for 20 minutes and then add potatoes and sausage. Bring to boil.