Better get to the Metropolitan Cafe early on Wednesdays, because the lunch special is crab cakes, and they sell like hotcakes, whatever that means. Unlike many Dallas restaurants that buy their crab cakes from food distributors, Metropolitan's Momma Christine makes these oval morsels from scratch, having divined her recipe from a dream, she says, as she did for many of the soups, salads, sandwiches and such that find their way onto the menu of this hot downtown spot. These babies are sautéed rather than deep-fried, loaded with fresh crabmeat rather than frozen and served up Texas-style with black-eyed peas and coleslaw. Lawyers, cops and journalists lousy for lunch turn away in tears when they learn there will be no more crab cakes until the following Wednesday. Unless, of course, they can dream up their own recipe.