The Cornish pasty is not a sandwich but it solves the sandwich's problem by building its own container, and the crimp is the part that makes it work. Instead of laying a filling between two slices, the pastry is rolled into a single round, loaded with raw beef, potato, swede, and onion, folded over, and sealed along one edge with a thick rope crimp. That crimp is structural, not decorative: it is the seam that holds a wet filling through a long bake, and it doubles as a handle, the sturdy spine you grip while the rest is eaten. The defining fact is that the bread is engineered to the cargo rather than the cargo fitted to the bread, which puts the pasty in the sealed-pocket family rather than the open-faced or stacked one.
The craft is in the pastry and the closure. The dough has to be strong, a sturdy shortcrust with enough structure to hold its shape and survive a coat pocket or a lunch tin, not a delicate flaky one that would shatter and leak. The filling goes in raw because the bake time is set by the crust browning, not the meat cooking, and the vegetables release moisture that steams the beef gently inside the sealed shell, so the pastry effectively becomes a small oven. The crimp must be pressed firm and unbroken, because a weak or split seam vents that steam, dries the filling, and fails on the walk to wherever it is being eaten. This was built for workers who needed a hot, self-contained meal that lasted a shift, and the whole design still shows that brief.
The variations stay inside the sealed, crimped frame. The cheese and onion pasty swaps the meat for a savoury vegetable filling but keeps the rope seam. A sweet pasty runs fruit or jam behind the same crust. The wider pasty and pie family, the Scottish bridie, the Bedfordshire clanger with its savoury and sweet ends in one roll, share the engineered-container logic from different regions. Each of those is its own thing and deserves its own article rather than being crowded in here.