The hot pastrami sandwich is decided in the steamer, not at the cutting board. Pastrami arrives already brined, rubbed in pepper and coriander, and smoked, but what makes the sandwich is the final steaming that takes the meat hot and slack: the fat goes silky, the muscle gives no resistance, and the slices arrive warm and yielding rather than firm and cold. It is then hand-sliced and piled onto two thin slices of rye with a swipe of yellow or brown mustard. That is the entire build, and the deliberate imbalance of it, a mountain of hot meat against barely any bread, is the point.
As a sandwich it works because every component is chosen to stay out of the meat's way. The rye is a seeded, faintly sour loaf, used in thin slices because its job is to give the hands a grip and the mustard a home, not to add bulk that competes with the pastrami. The slicing is done by hand and against the grain, thick enough that each slice has presence but tender enough that it folds rather than holds a flat edge: machine-thin slicing of steamed pastrami turns it to thread and the sandwich collapses into shreds. The mustard is the only seasoning the build adds, sharp and acidic, cutting the rendered fat so a stack this rich does not read as one heavy note. Heat is structural here, not a serving preference. Warm pastrami drapes and compresses into a sandwich you can pick up; the same meat cold would sit stiff and fall apart in the hand.
The hot pastrami belongs to the Jewish deli's smoked-meat counter, where the close relations differ by cure and by what gets added on top. Corned beef runs a leaner, boiled, brisket-based profile 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. Combination builds stack pastrami and corned beef together. Each of those is its own sandwich and deserves its own article rather than being crowded in here.