Melt 4 tablespoons butter in a large heavy saucepan over moderate heat and blend in 4 tablespoons flour. Add broth and 1 cup light cream or half-and-half and heat, stirring constantly, until thickened and smooth. Mix in salt, pepper, nutmeg or mace, parsley or chives, and 1 to 1½ cups diced turkey meat and (optionally) 1/2 cup diced, cooked carrots and/or 1/2 cup cooked diced potatoes; cover, let simmer over low heat for 15 minutes, then serve hot.