If you've never had a good black-and-white cookie, you won't understand why anyone would want to eat one. We've all been tempted by the two-tone discs the size of UFOs topped with dark-brown and white icing that call to us from behind the counter at every diner. But what's to like about a powdery, crumbly dome topped with a tasteless sugar glaze? Family Bakery, an outpost of Jewish Brooklyn and Queens circa 1965, produces a wonderfully moist, spongy marble cake, sweet and toothsome rainbow petits fours, and flaky bearclaws. Snowbirds who haven't seen a proper corn rye bread in years find it here. And the place has the best black-and-white cookies south of Sheepshead Bay. The icing's chocolate hemisphere is rich with cocoa, the white hemisphere a creamy vanilla. The big cookie underneath is a little lemony, a little cakey, but firm enough to hold up to a glass of milk. Take a number, take your place at the back of the line, and salivate in anticipation.