Cook the broth in a pot. If using smoked bacon, fry it in a pan and pour the fat into the broth. Add the smoked meat or bacon and cook for about 20 minutes.
Meanwhile, slice the white sausage into rounds. Remove the smoked meat from the soup and add the sliced sausage.
Once the sausage is cooked (about 10 minutes), slowly pour in the rye sourdough starter while stirring constantly. Bring the soup to a boil and cook for another 5 minutes. Be careful not to let it curdle.
Add the crushed garlic, marjoram, and optionally, grated horseradish to the soup. Season with salt and pepper to taste.