The combination is the deli's argument that two cures are better than one, stacked into a single sandwich. It is pastrami and corned beef piled together on the same two thin slices of rye, and the point is the contrast inside one bite: pastrami is brined, peppered, smoked, and steamed to a silky, spiced richness, while corned beef is brined and boiled to something leaner, cleaner, and saltier. Eaten side by side on the same fork they would be two sandwiches; interleaved in the same stack they read as one meat with two registers, the smoke and the boil alternating slice by slice. That deliberate layering is the whole sandwich.
The craft is in the slicing and the order. Both meats are cut by hand against the grain, thick enough to have presence and tender enough to fold, because machine-thin slicing turns either one to thread and a combination to a shapeless wad. The slices are shingled in alternation rather than dumped in two separate blocks, so no bite is all pepper-and-fat or all lean-and-salt; the stack is built to keep the two cures in conversation. The rye is a seeded, faintly sour loaf used in thin slices for the same reason it always is at this counter: its job is to give the hands a grip and the mustard a home, not to add bulk against an already enormous pile of meat. Mustard is the only seasoning the build adds, sharp enough to cut the pastrami's rendered fat without flattening the corned beef. Heat is structural, not optional: warmed, the two meats drape and compress into something liftable; cold, the stack stiffens and breaks apart in the hand.
The combination belongs to the Jewish deli's smoked-meat counter, where the close relations differ by cure and by what gets added on top. Hot pastrami and corned beef each run alone on the same rye. The Reuben griddles pastrami or corned beef with Swiss, sauerkraut, and Russian dressing into a hot pressed sandwich; the Rachel swaps the kraut for slaw. Each of those is its own sandwich and deserves its own article rather than being crowded in here.