Place the lentils in 1 1/4 litre of cold water and bring to the boil. Cover and cook over medium heat for about 40 minutes. In the meantime peel and wash the potatoes and cut them into sticks. Clean and wash the soup greens.
Cut leek into rings, carrots into slices, celery into sticks of the same size. Add sausage, carrots, potatoes and celery to the lentils and cook for another 15 minutes. Add the leek five minutes before the end of the cooking time.
Wash and coarsely chop the marjoram and parsley. Remove the sausage and cut into slices. Put it back into the stew. Season to taste with salt, pepper and vinegar, bring to the boil again and fold in the herbs.