Clean the leek and cut in half lengthways. Cut into pieces approx. 3 cm long, wash and drain well. Peel and finely chop the onion (s).
Heat butter or margarine and sauté the onion until translucent. Add the leek, mix with the salt and sprinkling seasoning and add water. Simmer over medium heat for about 30 minutes.
In the meantime, whisk the roux with milk and bring to a boil in a saucepan (approx. 5 minutes). Season the sauce with nutmeg and add to the leek vegetables.
Well suited as a side dish to pan-fried foods, potatoes and / or Brussels sprouts also go well.