Saute the leeks in the butter for 10 minutes. Add the potatoes, salt, and stock, and simmer until potatoes are tender, about 30 minutes. Strain the liquid from the solids. Puree the solids, adding back in enough liquid to keep moist, in batches in a food mill. Stir in the remaining liquid, and pass soup through a fine strainer. Add the half-and-half, nutmeg, and pepper. Adjust seasoning to taste. Chill well.Advertisement
Stir in cream to serve, and top with fresh chives, whole or chopped.