Discard tough outer stalks of the cardoon. Break off the tender, inside ones. With a potato peeler, peel the ribs, or strings, off the stalks, just like peeling celery.
Cardoons turn dark (like artichokes) when cut; to prevent this, rub the cut side of a lemon over the branches as soon as they are peeled. Cut into 2-inch lengths and put into water to which has been added Fruit Fresh (ascorbic acid). When enough stalks have been cleaned and cut to serve 4, lift them from the water and bring the water to a boil. Add salt to season the water and then add the cardoons. Simmer for about 1 hour, or until tender.
When done, drain. Melt chunk of butter in a skillet. Add cardoons and sauté for 5 minutes. Put into a dish. Stir flour into butter. Add salt, pepper, nutmeg, and sugar. Stir in milk and crème. Stir-cook until thickened. Taste and adjust seasonings.
Add cardoons, parsley, and chervil. Heat. Pour into serving dish, dot with butter, and serve.