Celebrity chef–sponsored food festivals seem to be a dime a dozen these days, but Ultimo at the Venetian Las Vegas, from December 5 through 7, is no ordinary food festival. Hosting the event and preparing food throughout the weekend is not one but three brand-name chefs—Daniel Boulud, Emeril Lagasse, and Buddy Valastro—and optional accompaniments to the dining festivities are spa treatments at the Venetian’s Canyon Ranch SpaClub, exotic-car driving at the nearby Las Vegas Motor Speedway, and a shopping spree w…