One of the world's most popular cocktails, the Martini has been made and served in a seeming infinity of ways. Purists attest that it can't be made with anything but a mix of gin and vermouth, but that hasn't stopped a surge of experimentation on the basic formula. Dry vermouth imparts a slightly herbal and bitter flavor to the green flavor of gin; while it's a classic counterpoint, it's not the only fortified wine in a mixologist's back bar. In New York City a few weeks ago, floating wine club The Noble Rot hosted a sherry party at which Mayur Subbarao, beverage director of the cocktail bar Cienfuegos, introduced a Manzanilla sherry where the vermouth usually goes. This style of fino sherry, from the coastal town of Sanlucar de Barrameda in Jerez, is light, briny, and bone dry — a playful substitute, tangy and crisp with a slightly salty flavor and long, nutty finish that entirely transformed my notion of what makes a martini, while still keeping a few flavor references to the classic version.