The pork scratching sandwich is a dare with bread around it. Pork scratchings are hard fried pieces of pork rind, the skin rendered and cooked until it is brittle, salty, and aggressively crunchy, normally a pub snack eaten by the bagful beside a pint. Putting them in a sandwich is a deliberate provocation: the entire build is a single argument about texture, a filling so hard it resists the teeth set against bread so soft it offers none. The point is not nourishment or balance. It is the contrast itself, taken further than good sense usually allows.
The craft, such as it is, is in managing that texture so the sandwich is eaten rather than abandoned. The scratchings are lightly broken rather than left in whole knuckles, because a flat layer of smaller shards can actually be bitten through where a single hard lump just shifts and defeats the bread. They are intensely salty and pure fat, so the bread is soft white loaf buttered to the edges, a yielding cushion that takes the impact and a fat that the salt has something to sit against. No sauce is essential, but a smear of mustard or brown sauce cuts a filling that is otherwise all salt and crunch, and a few crisp shreds of lettuce or pickle give the one note something to play against. There is no heat and no assembly to speak of: the whole sandwich is the decision to do it at all.
The variations are few and stay true to the dare. Scratchings with brown sauce is the standard concession to flavour; lightly crushed into a softer rubble with mustard is the version actually engineered to be eaten; alongside a wedge of strong cheese it tips toward a pub-snack ploughman's. The wider cold-cut and pub-snack shelf handles pork in gentler forms. Those deserve their own article rather than being crowded in here.