In seventeenth-century France, meat wasn't considered ready to eat until it, well, stunk. You couldn't get that past the health inspectors these days, but Louis XIV was onto something: The secret to really great beef is aging. Which is why sides of cow hang on their hooks in Widmer's cavernous refrigerator for at least two weeks before they're sliced into the ruby-red, fork-tender sirloins, ribs, and rounds that tempt you from under the 20-foot glass counter--at prices, mind you, that easily beat some of the larger stores: The butter-knife-soft tenderloin was recently on special for $7.99 per pound. Even the hamburger is made from top-quality cuts, without the "filler" meats other butchers like to grind up. Tip for Y2K worriers: Upon request, owner Steve Korte will sell you a whole hindquarter, aged and sliced and neatly packaged in old-fashioned freezer paper. Just don't let the neighbors know.