The Frogmore stew sandwich takes a South Carolina Lowcountry boil, a communal pile of shrimp, smoked sausage, corn, and potato dumped on newspaper, and forces it into a roll, which means the defining problem is structural before it is anything else. A boil is loose by design: separate pieces, no binder, eaten by hand off a table. A sandwich needs those pieces to hold a line long enough to be lifted. How the boil is cut down and bound without losing the point of a boil is the whole craft, and it is the reason this is an unusual sandwich rather than an obvious one.
The craft is in reducing the boil to something a roll can carry. The shrimp are peeled and the sausage and corn are cut off the cob and into bite pieces, then the mix is bound just enough, a little mayonnaise or butter, sometimes the spiced boil liquid reduced and clung to the solids, so the filling holds together without becoming a salad. Old Bay or a Lowcountry boil spice stays on the shrimp and sausage rather than being washed off, because that seasoning is the entire flavor of the dish and the bread has none. The roll is a soft split bun or a sturdy hoagie chosen for grip, not character: it has to soak the spiced fat and stay liftable under a wet, loose, heavy filling without folding in the middle. The smoked sausage does structural and flavor work at once, firm enough to anchor the soft shrimp and corn around it. This is dock and roadside food, assembled fast off whatever the boil produced, eaten immediately while the filling is warm and the bread has not yet given way.
The variations follow the boil rather than a recipe. A warm-butter build serves it hot with drawn butter instead of a cold bind. A version that crisps the sausage adds a firmer counter to the soft shrimp. These belong to the dense regional specialty shelf tied tightly to one stretch of coast, and each deserves its own article rather than being crowded in here.