Peel and chop the onion. Peel, wash and roughly dice the potatoes and carrots. Clean, wash and roughly dice the carrots. Heat the oil in a pot, fry the onion, potatoes, bay leaf and carrots briefly. Deglaze with broth, bring to the boil, cover and cook over medium heat for about 15 minutes.
In the meantime cut the sausages into slices. Wash parsley, dab dry and chop. Add lentils and sausages to the soup, bring to the boil and cook for another 5 minutes. Season to taste with salt, pepper, sugar and vinegar. Serve the soup sprinkled with a dash of herb crème fraîche and parsley