The Corned Beef Sandwich is the deli classic as it appears on Israeli counters, brined beef sliced and built into bread, and it hinges almost entirely on the meat. The angle is the cure and the cut. Corned beef is brisket brined with salt and spice until it is pink, salty, and yielding, so the sandwich is a frame for that meat rather than a contest of fillings: get the slicing, the bread, and the sharp counterpoint right and it reads as a clean, deeply savory deli sandwich; get them wrong and it is either dry and salty or a thin token of meat lost in bread and condiment.
The build is short and the margins are tight. The corned beef is cooked low and slow until a fork goes through it, then sliced across the grain so it pulls apart rather than chews tough. The bread is a structural decision, most often rye or a sturdy white, strong enough to hold a real pile without going soggy from the meat's moisture. Mustard is the standard accent, sharp and acidic against the salt of the cure, and pickle usually rides alongside for the same reason. Done right, the meat is warm or barely cool, tender, sliced thin enough to fold, salty but not punishing, with the mustard cutting cleanly through every bite. Done wrong, it is sliced thick with the grain so each bite is a fight, dried out from sitting, oversalted to the point the beef flavor disappears, or stacked so high the bread fails and the sandwich collapses.
It varies mostly by bread, temperature, and what goes on with the meat. Cold on rye with mustard it is the lunch-counter standard; warmed and pressed it edges toward the grilled deli direction; piled with sauerkraut and dressing it crosses into Reuben territory, which is its own order and deserves its own treatment. The pastrami sandwich is its closest neighbor, the same brisket pushed further with a peppered, smoked crust, and it too earns separate handling. What stays constant under every version of the corned beef sandwich is the demand on the core: brined beef tender and well sliced enough that bread and a sharp mustard are the entire sandwich.