The singin' hinny is the rare entry on the British sandwich shelf where the bread is the whole event and the filling is barely an afterthought. It is a large griddle cake of the Northeast: flour, lard or butter, currants, a little sugar, and just enough milk to bring it together, cooked flat on a hot bakestone or heavy pan rather than baked in an oven. The name comes from the sound it makes on the heat, the fat sizzling and the dough singing as it cooks, and that is the right way to understand it. This is not a loaf pressed into sandwich duty. It is a griddle cake whose entire reason for being a sandwich is the moment it comes off the stone, gets split while still hot, and has cold butter pushed into the steaming crumb.
The craft is the griddle and the split. A cake this size has to cook through on a dry heat without the outside scorching before the centre sets, so the bakestone is held at a steady moderate heat and the cake is turned once, browned and freckled on both faces, the currants kept just short of catching. The split is done by hand and done hot, the cake torn or cut across while it is still too warm to hold comfortably, because the point is that the butter melts on contact and soaks into an open, slightly crumbly interior rather than sitting on a cooled surface. Salted butter is the only thing that goes in, and it goes in generously, the salt set against the sweet fruited crumb the way salt is set against sweetness across the whole British sweet tradition. Anything more would be working against a cake that is already seasoned and rich enough to stand on its own.
The variations stay inside the griddle-cake frame and change only what is around the butter. A plain version drops the currants for a faster, less sweet cake closer to a griddle scone. A thin scrape of jam or honey on the buttered half pushes it further toward a tea-table sweet. A wedge of a firm regional cheese laid on the warm split half turns the balance savoury, the same sweet-against-sharp instinct that runs through the Northeast's baking. Each deserves its own article rather than being crowded in here.