Sourdough Sandwich

On Stoney Street at Borough Market, the Kappacasein stall presses its toastie between slices of Poilâne sourdough, and the first minute at the iron explains why the bread was chosen. Montgomery's cheddar, Comté and Ogleshield go in with chopped onion and leek, and as the plate comes down, the cheese that escapes the slices fries against the hot metal into a lacy brown edge. The crust crackles under the first bite, the open crumb gives behind it, and the sour note lands on the sweetness of the leek while the cheese stretches in long strings between mouth and plate. Eaten standing in the market lane, it burns the roof of the mouth for the first few bites, and nobody waits.

Sourdough raised by a wild culture bakes with a thick blistered crust and a crumb full of irregular holes, and the toastie has to work with both. A slice cut too thin shatters before the filling is in; one cut too thick turns the sandwich into a jaw workout and shoves the cheese to one side. Butter on the outside, or a spread thick enough to fill the holes, stops a wet filling from soaking through and tearing the slice along them. Under the press the crust turns brittle and the holes close around melted cheese, so the whole slice holds its shape in the hand and the filling stays put until the last bite.

Ogleshield is a Somerset washed-rind cheese that melts into a smooth, savoury pool, Comté adds a nutty sweetness, and Montgomery's cheddar carries the sharp, grassy edge that stands up to the sourdough's acidity. Onion and leek, chopped fine, cook down inside the cheese until they turn jammy. The same logic runs through London's newer toasties. When Jason's Sourdough launched its toastie range on 1 October 2024, the ham hock version came with mature Cornish cheddar on sourdough ciabattin, alongside an nduja version and a kimchi one.

Cold, the same bread asks for gentler handling. A sourdough sandwich assembled at a bakery counter, with salted butter, a few slices of ham or a wedge of mature cheddar and a spoon of pickle, wants a medium-thick slice from a loaf a day or two old, when the crumb has firmed enough to slice cleanly and carry the filling without squashing into dough. Grains-and-seeds loaves add a nutty crunch and a darker sour edge, while rye-blended loaves go denser and tarter and suit smoked fish. The crust takes some chewing whichever loaf it is, and that resistance slows the eating down.

The same sandwich is a kitchen habit. A frying pan or a sandwich press, a knob of butter, two slices off a bakery loaf and a handful of grated cheddar or leftover ham make a hot lunch in about ten minutes. The buttered outside fries golden while the cheese melts into the crumb, and the kitchen fills with the dry scrape of a knife on crust and a smell of browning butter and toasted sour dough with a sharper edge underneath. Home cooks tend to drop the leek, and the toastie comes out as good as the pan is hot.

Origin and history

Bill Oglethorpe grew up in Zambia, studied at an agricultural school in Switzerland, learned cheesemaking on a farm in Provence and then worked for Neal's Yard Dairy before setting up Kappacasein on his own. His Borough Market stall sells raclette, with the cheese melted over new potatoes, gherkins and pickled onions, and a toastie that Neal's Yard Dairy calls the unofficial Best Toastie in Town.

The cheese behind both comes from Kappacasein Dairy, under the railway arches on the Voyager Industrial Estate in Bermondsey. Milk from Kent is heated in a copper vat of about a century old, the curd is cut and squeezed in cloth, and the wheels mature for up to a year, stamped Bermondsey. The stall sits at the end of that chain, and the toastie is where the dairy's cheeses meet a customer in the lane.

Oglethorpe has been making and selling the toastie at the market since 2003, long before sourdough toasties turned up on high-street menus, and the recipe he shares has kept the same pairing of Poilâne sourdough and Montgomery's cheddar throughout.