The Cornell chicken sandwich is the chicken sandwich with no crust to defend, because the bird is grilled rather than fried and the entire sandwich is built around a marinade instead. The defining element is the Cornell sauce: a thin, sharp emulsion of cider vinegar, oil, egg, and poultry seasoning that the chicken sits in before it ever touches the grill and gets brushed with all the way through cooking. It is a barbecue sandwich whose flavor lives in an acid bath, not a smoke ring or a fryer, and on a soft bun that distinction is the sandwich.
The craft is in the marinade chemistry and the grill discipline. The egg in the sauce is doing real work, holding the oil and vinegar in suspension so the mixture clings to the chicken in a thin coat rather than running off, basting it without ever building a glaze. The vinegar penetrates and seasons the meat deeply while keeping it moist over open heat, which is the whole reason a grilled chicken sandwich here does not read as dry the way a bare grilled fillet usually does. The chicken is cooked over coals long and turned often, brushed at every turn, so the surface picks up char and the interior stays loose and tart. The bun is plain, soft, and almost incidental: it is there to carry a sharp, juicy piece of bird and absorb the sauce that runs, not to add texture or stand up to a crust, because there is no crust. The lunch-counter and fair-stand reality is a grill of split chicken halves worked in rotation, a bucket of sauce and a brush in constant motion, the sandwich pulled off, sauced once more, and closed on the bun to order.
The variations stay close to the sauce. The split-half plate is the same chicken eaten off the bone rather than in bread; bumping the cayenne or the poultry seasoning shifts the marinade's edge; some builds add a thin slaw for crunch the grilled meat lacks. These are small turns on a sandwich defined by one acidic baste, and the broader fried chicken argument, the chain fillets, the Nashville hot crust, the Korean double-fry, is doing the opposite of what this one does and deserves its own articles rather than being crowded in here.