The Alabama white sauce chicken sandwich is built around a barbecue sauce that contains no tomato at all. Where the fried chicken sandwich usually answers richness with a sharp pickle and a thin condiment, this one answers smoke and char with an emulsion: mayonnaise loosened with cider vinegar and cut with coarse black pepper and cayenne. That pale, tangy sauce is the defining component. It is poured or brushed onto smoked or grilled chicken so it both seasons the meat and slicks it, which is the whole reason a lean bird on a bun does not read as dry.
The craft is in keeping the sauce an emulsion and the chicken juicy. The white sauce lives or dies on the ratio of mayonnaise to vinegar: too thin and it runs off the meat and floods the bread, too thick and it sits on top as a paste instead of working into the chicken. It is acidic and peppery on purpose, because its only job is to stand against smoke, char, and fat, and a timid version disappears. The chicken is cooked over heat until the surface takes color and then dressed while still warm, so the sauce clings to a hot surface rather than sliding off a cooled one. The bun is the same problem every sauced-chicken sandwich poses: soft and slightly sweet so it yields to the fillet, with the sauce applied so the bread carries flavor without dissolving before the last bite. Shredded lettuce or a thin slaw and a pickle are the standard counter, the cold crunch and extra acid a warm, sauced fillet has none of, and the sandwich is assembled and eaten while the chicken is still hot.
The variations track the cut and the cook. A smoked, pulled version soaks more sauce and eats looser; a grilled fillet keeps a firmer bite and a cleaner char; a fried fillet under the same white sauce borrows the crust of the standard fried chicken sandwich and tests it against a wet dressing. The sauce itself travels onto smoked turkey and pork, where it behaves differently against a different fat. Each of those is its own preparation and deserves its own article rather than being crowded in here.