Cook the white sausage: Bring the broth to a boil, when hot add the raw white sausages and simmer over very low heat for 15-20 minutes. The broth should not cook rapidly, it should just gently simmer.
Chop the smoked bacon into 1/2-inch (1 cm) cubes, press the garlic through a garlic press. Peel the potatoes and cut them into small cubes.
When the sausage is cooked, take it out of the water and cut into slices.
Add potatoes to the broth and cook for 7-10 minutes or until the potatoes are soft.
Heat the oil in a large frying pan. When hot, add the sausage slices and bacon. Cook for a couple of minutes over medium-high heat, until they are browned on all sides. Add the garlic and marjoram and cook for 30 seconds.
Add some hot broth to the pan then scrape with a spatula all the brown bits on the bottom of the pan. Add the content of the pan to the pot with broth.
Add the sour wheat starter - stir the flour with the liquid and add it to the soup. Make sure to add the starter gradually – trying the soup while you add it, to make sure it’s not too sour for you.
Add the heavy cream and horseradish. Warm up the soup until very warm (I'm trying not to boil it only to preserve the health benefits of the wheat starter).
Season the soup with salt and pepper. Serve with hard-boiled eggs.
Enjoy!