The pilchard sandwich is built on what comes out of the tin. Pilchards are large sardines, and the tinned ones are packed in tomato sauce, the fish soft enough to break under a fork and the sauce already seasoned and faintly sweet. That is the whole filling and the whole appeal: an oily, strong, cheap fish in a ready-made sauce, mashed onto bread with nothing much added. It belongs to the same store-cupboard thrift as paste from a jar, a sandwich made from a tin that lives in the back of the cupboard for exactly this purpose.
The craft is managing oil and softness against plain bread. The fish is drained of the loosest sauce and roughly mashed, bones and all, because tinned pilchard bones are soft and the mash is the texture the sandwich has; left whole, the fillets slide and the sandwich falls apart in the hand. A little of the tomato sauce is worked back through for moisture and a squeeze of lemon or a grind of pepper cuts the oiliness, which is the one thing a strong tinned fish needs and the one correction that keeps it from reading as flat. The bread is soft plain loaf, buttered to the edges so the oil does not soak straight through, because the point is a firm carrier against a soft, wet filling rather than anything with chew of its own. Pressed and cut, it is a sandwich made in a minute from a tin and a loaf.
The variations stay close to the tin. A scrape of vinegar or a few drops of malt sharpens it further; sliced raw onion or cucumber adds a crisp counter to an all-soft filling; mashed with a little mayonnaise it goes smoother and milder, closer to a paste. Its relatives are the sardine, kipper, and mackerel sandwiches of the same oily-fish shelf, each a different catch met with the same restraint. Those deserve their own article rather than being crowded in here.