The chopped liver sandwich is held together not by the liver but by the schmaltz, the rendered chicken fat that turns a coarse, mineral, crumbly mince into something that spreads and binds. Chicken livers cooked and chopped with sautéed onion and egg are, on their own, dry and dense and inclined to fall apart on the bread. Schmaltz is what makes it a sandwich filling rather than a pile: it carries the iron-heavy flavor of the liver, it lubricates the mince so it holds to rye or challah instead of crumbling out the sides, and it ties the onion's sweetness and the egg's softness into one cohesive spread. That fat is the engineering decision the whole sandwich rests on.
The craft is in the chop and the bread. The livers are cooked through but not past the point where they go grainy, then chopped by hand rather than pureed, because the texture is supposed to read as a coarse mince with the onion and egg still visible in it, not a smooth pâté. The schmaltz is worked in warm so it distributes evenly and sets the spread firm once cooled. The bread is the counter to a rich, heavy, single-note filling: a seeded sour rye gives acid and chew that cut the fat, while challah goes the other way, soft and faintly sweet, leaning into the richness rather than against it. The choice is a real one and it changes the sandwich. A thin smear of mustard or a few rings of raw onion are the only additions the spread needs, because anything more competes with a filling that is already dense and assertive. It is a deli-counter build that can be made ahead, held cold, and cut to order without losing its structure, which is part of why it earned a place on the same counter as the corned beef and the pastrami.
The variants are bounded and honest. The rye build and the challah build are effectively two sandwiches sharing a name; a layer of chopped liver inside a combination deli sandwich folds it into a larger stack; a richer version pushes the schmaltz and onion further toward the appetizer plate it descends from. It belongs to the lunch-counter classics alongside the egg salad and the tongue sandwich, and those relatives deserve their own articles rather than being crowded in here.