An extra mature Cheddar sandwich is built around a cheese that has changed physically with age, and the texture is the lead, not the flavour. A long-aged Cheddar is drier and harder than a young one and carries small crystalline specks through its body, the gritty crunch that registers under the teeth as a faint, deliberate resistance. That crunch is not a flaw and not seasoning; it is the cheese itself, and a sandwich built on extra mature Cheddar is a sandwich organised around protecting and presenting it. A milder block would melt softly into the same bread and disappear. This one is meant to be felt.
The craft is the cut and the restraint, because an extra mature Cheddar is loud and the build's job is to stay out of its way. The cheese is sliced rather than grated, and cut on the thicker side, because a long-aged Cheddar that is shaved too thin loses both its crystalline texture and the acidic, almost peppery sharpness that is the entire reason to choose it. That sharpness is the only seasoning the sandwich needs and usually the only one it should get: a strong pickle or a sweet chutney, useful against a gentle Cheddar, here competes with a cheese that is already at full volume and flattens the very edge that defines it. Butter to the edges remains structural, waterproofing the crumb and carrying the cheese's salt across the slice, and a few minutes out of the fridge matters more than with a soft cheese, because a long-aged Cheddar straight from the cold is hard and waxy and mutes the very sharpness it was aged to develop. The bread is soft and plain so nothing argues with a filling that is doing all the talking.
The variations are mostly the question of whether to add a counter to a cheese this assertive or let it stand alone. A thin smear of a mellow fruit chutney can frame the sharpness without burying it; a vintage or cave-aged version pushes the crystalline crunch and the acidity further still; the bare bread-and-butter reading is the cheese with absolutely nothing in front of it. Each tips the sandwich toward a named build with its own logic, and those deserve their own articles rather than being crowded in here.