Jack in the Box's Smashed Jack is a thin, crispy-edged beef patty smashed on the grill with melted American cheese, pickles, onions, and a buttery sauce on a brioche bun. Jack's entry into the smash burger trend that's taken over fast food, it competes with Shake Shack's ShackBurger and Culver's ButterBurger as a premium thin-patty option.