Peel and quarter the onion. Boil up the porcini mushroom stock, peas, onion and marjoram in a pot. Cover and cook on low heat for about 1 hour. Stir from time to time. In the meantime clean and wash the soup greens and potatoes. Dice celery and potatoes, cut leek into rings, cut carrots into short sticks. Wash parsley, dab dry and chop.
Cut sausages diagonally into thin slices. Add parsley, except for a tablespoon, to the finished pea stew and puree everything. Season the stew with salt and pepper, add the vegetables and simmer for another 10 minutes. Stir from time to time. Finally, add the slices of sausage to the stew and warm them up. Season stew again, arrange in deep bowls and sprinkle with remaining parsley. Serve garnished with marjoram as desired