Peeled prawns and a light dressing, and the sandwich lives or dies on the ratio between them. The prawns are cooked, shelled, and kept whole or roughly halved, sweet and faintly briny with a clean snap. The dressing is usually a mayonnaise, sometimes lifted toward the pink, tomato-and-spice register of a cocktail sauce, just enough to coat and bind without burying the shellfish. The defining element is that ratio: enough sauce to carry the prawns across the crumb, never so much that the sandwich becomes dressing with prawns in it. The bread is a split crusted loaf or a soft buttered roll.
The craft follows from how delicate the protein is. Prawns are mild and a touch sweet, and they go rubbery and dull if overworked or overdressed, so the build keeps the binder thin and the seasoning simple: lemon, a turn of pepper, maybe a few crisp leaves for contrast and a little salt to lift the sweetness. A cocktail-style sauce earns its place when it stays restrained, its acidity and faint heat sharpening the prawns rather than coating over them. The sandwich is eaten cold and soon, because shellfish in dressing does not hold well and the texture turns the longer it sits. The bread needs a real crust because the filling brings moisture and richness but no structure of its own; the crust is what keeps the sandwich from going slack.
Variations stay close to the prawn. The same filling goes into a softer milk roll for a gentler, more buttery read, or onto firm seeded bread when the kitchen wants the grain to push back against the dressing. Crème fraîche sometimes replaces part of the mayonnaise for a cleaner, slightly tart finish, and a stripe of fresh herb or a leaf of crisp lettuce is a common single addition. The Sandwich aux Crevettes belongs with the cold-water seafood builds the catalog groups under Baguette Poisson. Its specific contribution to that shelf is sweetness handled with a light hand: a mild protein the sandwich frames and dresses just enough to hold together.