Soak the peas overnight in 2 litres of cold water.
Onions peel and chop finely. Wash herbs, shake dry and chop. Heat the oil in a large pot. Fry the onions in it. Add 1 l cold water and peas together with soaking water. Bring to the boil and remove any foam that has formed. Add herbs. Simmer covered for about 1 hour.
Clean or peel and wash the soup greens. Finely dice carrots and celery. Cut leek into fine rings. Peel, wash and finely dice potatoes. Add everything to the soup. Season with salt and pepper. Bring to the boil and simmer covered for about 30 minutes. Stir several times.
Whip the cream until semi-stiff. Stir in horseradish. Pick salmon. Season soup with salt and pepper to taste. Serve with horseradish cream and salmon.
If not all guests like fish, serve the stremel salmon separately. Also air-dried ham goes well with it.