Peel and roughly dice the onions. Peel and cut the potatoes into eighths. Peel the carrots and cut into slices. Wash and chop the parsley.
Sauté the onions in the butter in a high pan, then add the potatoes and cook covered over a mild heat for 10 minutes. Then add the carrots and stock and cook for another 15 minutes.
In the meantime, fry the sausages in the oil in a second pan. When done, remove the sausages and cut into pieces.
Add the mustard and cream to the vegetables and briefly bring to the boil. Add the sausage, sugar, salt and pepper and season the stew to taste.