Cook the white sausage: Heat the broth, when hot add the raw white sausages and simmer over very low heat for 15-20 minutes (if you have already cooked sausage omit this step and just slice them like in the next step).
Chop all the meats: Take the sausages out of the broth and cut them into slices. Cut the smoked sausage into ½-inch cubes and bacon into small cubes.
Brown all the meats: heat the oil in a large frying pan. When hot, add all the chopped meat and sausages. Cook over high heat for a couple of minutes until nicely browned. Add all the meats to the pot with broth.
Dice the onion, press the garlic through a garlic press, peel the potatoes and cut them into 1-inch chunks.
Cook the onions, garlic, and marjoram: Add the onions to the pan and cook over medium heat for a couple of minutes or until soft and translucent. Add the garlic and 1 TBSP of marjoram and cook for 30-60 seconds more, until fragrant. Transfer the onions into the pot. Add a couple of tablespoons of broth to the pan and scrape with a spatula all the brown bits from the bottom of the pan, add them to the pot.
Cook the potatoes: Add the potatoes to the pot with broth, meat, vegetables. Bring the soup to a boil and cook over low heat for about 15 minutes or until the potatoes are soft.
Add the sour rye starter. Stir the flour with the liquid and add to the soup (any remaining spices should be discarded). Add the starter gradually, tasting the soup to make sure it’s not too sour for you (it’s completely acceptable to add the whole batch, just according to taste). Bring to a boil and simmer for a few minutes.
Add the cream to the soup. Add the horseradish.
Season the soup with salt, pepper, and the reserved ½ tsp of marjoram – rub the marjoram between your palms to release its aroma.
Serve the soup with sliced boiled eggs.