This herb-scented bechamel sauce is a lighter but luscious alternative to a rich cream sauce. Though thickened with flour, it has the texture of cream, and when cooked the full length of time it shouldn't have a floury taste. Always prepare this sauce before making the ravioli so the herb flavors have a chance to infuse. * Recipe excerpted from The Savory Way (Broadway Books, 1990), by Deborah Madison