The gold standard for brisket has long been set by the pitmasters of Central Texas, at places like Kreuz Market and Louie Mueller Barbecue, which got their start in the last century as German-American smokehouses. A pilgrimage to Central Texas, where the meat is served plain on butcher paper, is obligatory for brisket newbies. But New York’s pitmasters agree that the current passion for local brisket is fueled by a young colleague in Austin, Tex., Aaron Franklin, whose Franklin Barbecue has parlayed expertise, an urban location and a canny use of social media into cult status just five years after it began in a trailer with a walk-up window.