Soak peas over night in 2 liter water.
Next day cook peas on low heat in same water for at least 2 hours.
Chop onions fine, slice carrots, leek, cut celery root in cubes, peel potatoes and cut in cubes.
Add to peas together with bay leave and marjoram; add some broth if needed.
Let cook for another 15-30 min. Peas should be very soft.
In a pan fry bacon with 2 tbsp of chopped onions and the slices sausages for 1-2 min (you can only fry the bacon crunchy if you like and add the sausages as whole to the soup).
Chop parsley, with spices, vinegar and mustard add to soup.
Bring again to a brisk boil.