This is the loaded one, the full breakfast compressed into a single roll: bacon, sausage and a fried egg together, the sandwich often called the builder's breakfast because it is built to be a working morning's whole meal eaten in one hand. Where the plain bacon roll is defined by which regional bread word it answers to, this version is defined by the load itself. Three substantial elements, each with its own fat and its own behaviour, have to be made to sit in one roll and survive being picked up. That engineering problem is the sandwich. The bread is still the regional variable underneath, but here it is doing structural work the single-filling rolls never ask of it.
The craft is order and restraint inside a roll that has to hold all three. The sausage is cooked through and usually split or flattened so it lies flat instead of rolling out of the bread. The bacon is fried until its fat has rendered and the edges have caught. The egg is the difficult element: fried with the yolk firm enough to be picked up but soft enough to be worth having, and placed so a broken yolk runs down into the sausage and bacon rather than straight out of the side. The roll has to be soft enough to compress around the stack but substantial enough not to give way under the combined weight and fat, which is why this build leans on the firmer regional rolls more often than the plainest bap does. Butter still bridges salt and bread; sauce, brown or red, still goes inside; the whole thing is closed, pressed gently to settle the layers, and eaten before the egg and the steam have softened the base past holding.
The loading does not stop at three. Black pudding folds a region's breakfast into the same roll, square or Lorne sausage stands in for the round one across Scotland, a tattie scone or a hash element gets pressed in alongside, and the Ulster fry rebuilds the whole idea around its own components. The bread underneath still shifts with the map: bap, barm, cob, batch, morning roll, stottie, butterie. Those deserve their own articles rather than being crowded in here.