“Raviolo” is singular of “the much more common Italian word “ravioli,” and says that you only get one of them. That’s plenty enough in this case. The pasta part is a five-inch-square sheet, folded over some lump crabmeat in an uncomplicated but very good sauce involving shiitake mushrooms, spinach, unsweetened mascarpone cheese, and a creamy-looking citrus beurre blanc with a sprinkling of green onions. The crabmeat is the center of attraction. Even though it plays solo, one of these is big enough to split, or to make a light entree. I think this has been on the menu since before the brilliant Christopher Lynch took over as executive chef, but it’s right up to his level of cookery.