Back in 1925, railway worker Big Bob Gibson dug a pit in his backyard in Decatur, Alabama, nailed a plank-oak serving table to a sycamore tree, and started smoking barbecue for friends, co-workers, and passersby. One of Big Bob's specialties was hickory-smoked chicken, for which he devised a tangy, mayonnaise-based white sauce spiked with horseradish, vinegar, and cayenne that proved wildly popular, eventually spreading to barbecue joints throughout the region. Today, at Decatur's two Big Bob Gibson Bar-B-Q restaurants, a fourth generation of Gibsons oversees the brick-lined pits where butterflied chickens are smoked until juicy and browned. After that, they're dunked in the white sauce and served dripping with it. For our version of Big Bob's chicken sandwich, we baste the meat with the signature sauce during the smoking process, which adds another layer of flavor, then serve the meat, pulled away from the bone, on a soft, sesame seed bun with pickle chips and another dollop of that fine substance.