Pre-heat a large soup pot over medium-high heat with two turns of the pan of oil. Add the sliced knockwurst and cook until lightly browned, about 4-5 minutes.
Remove the browned knockwurst to a plate and add the caraway seeds to the pot. Toast for about 30 seconds, then add the onion, bay leaf and red cabbage. Season with a little salt and pepper and cook, stirring frequently for five minutes or until the onions and cabbage start to get tender – put a lid on it to get it really going.
Add the sugar and apple cider vinegar, cook for about one minute, then add the chicken stock and tomato sauce. Bring up to a bubble and simmer the soup for about 10 minutes. Add the knockwurst back into the soup and simmer another minute just to heat it up again.
While the stoup is cooking, combine the apple slices, lemon juice and parsley in a bowl. Serve the stoup topped with some of the thinly sliced apple mixture on top of each serving and some lightly buttered dark bread with raisins alongside.