Peel and finely chop the onion. Clean, wash and cut the leek into rings. Fry onion and leek in hot oil for about 3 minutes. Add sauerkraut and braise for about 5 minutes.
Add bay leaf and juniper berries. Pour in broth, stir in tomato paste and bring to the boil. Sprinkle in purée powder. Cut the sausages into slices, add to the soup and heat for about 5 minutes.
Season soup with salt, pepper, paprika and sugar. Add crème fraîche as a blob.