The double-dipped roast beef burger is an icon of Brooklyn, New York, and Burger Scholar George Motz is here to teach you how to make one at home. This regional one-off burger—known locally as the "Gargiulo"— hails from the historic roast-beef emporium Brennan & Carr. Here, the burger patty is topped with freshly sliced roast beef, sauteed onions, American cheese, and is eventually dunked in a vat of piping hot beef broth.