Onions peel, halve and in strips cut. Peel and finely dice the potatoes. Heat the oil in a large pot. Sauté onions for 1-2 minutes. Add 2 1/2 litres of water, stock and spices and simmer for about 5 minutes.
Place the sauerkraut in a sieve and rinse briefly under cold water, then chop a little. Add the sauerkraut and diced potatoes to the stock and simmer for 10-15 minutes. Wash parsley and dab dry.
Cut the leaves into fine strips. Halve the peppers, clean, wash and cut into strips. Add the paprika and parsley to the soup. Simmer again for another 5-8 minutes. Season soup with a little salt and pepper.
Garnish with parsley before serving.