Peel the onions and cut them in half. Mix wine with vegetable soup, add salt and boil. Pour in onions and cook for 15 to 20 minutes on a gentle heat.
Clean the leeks and cut them into rings about two centimeters wide. Cook with the onions and mustard seeds for 10 to 15 minutes. Pour into a sieve and collect the liquid.
Heat butter. Sauté flour in it, add 600ml vegetable water (for 4 servings) and cook for about 5 minutes. Add whipping cream, bring to boil repeatedly and season with pepper, whole sugar, mustard and nutmeg. Add onion and leek.
Serve with baked potatoes.