After five years of satisfying customers with his famous black-pepper crabs ($11.95), Kim Son owner Tan La became concerned that the restaurant's most spectacular menu item was becoming passé. So he sent his mother back to Vietnam to find another crab recipe. She returned with one for tamarind crabs ($11.95), a dish introduced last year that marries Kim Son's plump, succulent crabs with a sweet and tart sauce rendered from the fuzzy, knobby tamarind bean. The crabs are stir-fried in the oh-so-sticky sauce and served up, usually four to a platter. No matter how many extra napkins they provide, it's not enough. You don't want to miss any of the sweet meat tucked strategically inside the crustacean, but the sauce itself is so good you may find yourself licking the shells -- and your fingers, again and again. After a meal of these, you'll find yourself wishing Kim Son had just one more thing: a shower.