The pastie bap is a Northern Irish chip-shop sandwich, and the fried pastie inside it is the defining fact, not the bread around it. An Ulster pastie is not a baked pasty: it is a flat round of seasoned minced meat, potato, and onion that is bound, shaped by hand, dipped in batter, and deep-fried at the chip shop alongside the fish. Put that hot fried disc into a soft buttered bap and the build is complete. The whole identity sits in the order of operations: the filling is cooked and crisped in batter first, then carried by the bread, so the bap is a wrapper for something that already has its own shell rather than a structure doing any work of its own.
The craft is the contrast between a battered, greasy, just-fried interior and a plain soft exterior, and the logic is the same carbohydrate-on-carbohydrate reasoning that runs through the chip butty. The bap is chosen soft and faintly sweet because the pastie brings all the salt, all the crunch, and all the fat, and a chewy crust with real resistance would only fight a filling that has no give to spare. Butter on the bap is structural: it bridges the salt of the fried batter to the wheat of the bread and seals the crumb a little against the grease so the bap does not collapse to paste before the last bite. It is eaten straight from the wrapper while the batter is still crisp, because a pastie that has sat and gone soft inside the bap has lost the one texture that justified frying it.
The variations stay inside the chip-shop window. Brown sauce or red sauce is the genuine divide, applied inside the bap so it does not run through the batter and soften it; a pastie supper takes the same fried pastie with chips instead of bread; a battered sausage or a fish gets the identical soft-bap treatment off the same fryer. Each deserves its own article rather than being crowded in here.