Challah (חלה) is the braided, enriched egg bread of the Jewish table, and within a sandwich catalog it matters as a bread first: a soft, slightly sweet, tender-crumbed loaf that becomes a distinctive sandwich base when sliced. The angle is what that crumb does to a filling. Challah is richer and softer than a standard white loaf, with a glossy thin crust and an interior that tears in strands rather than crumbs, so a sandwich built on it leans toward the soft, slightly sweet, almost pastry-adjacent end of the spectrum. That is a strength with the right fillings and a liability with the wrong ones.
The bread itself is the build here. The dough is enriched with egg and oil and lightly sweetened, then divided into strands and braided, most commonly into a three or six-strand plait, sometimes coiled into a round. It is proofed until airy, washed with beaten egg for a deep shine, often topped with sesame or poppy seed, and baked until the crust is burnished and the inside is feather-soft. For sandwich use it is sliced thick, since a thin slice of such a tender crumb tears under any spread. Done well, the slice holds its shape, the crust gives a faint chew against a pillowy interior, and the slight sweetness frames a filling rather than fighting it. Done badly, the loaf is dry and dense from underproofing or too little fat, the crumb is so soft it pulps the moment a wet filling touches it, or the sweetness is pushed so far that it clashes with a savory build. Day-old challah is often the better sandwich bread precisely because a little staling firms the crumb enough to hold up.
As a sandwich base its behavior shifts with the filling and the slice. It is a natural partner for rich, soft, mildly sweet fillings, egg salad, tuna salad, soft cheese, smoked fish, where its tenderness and faint sweetness are an asset. It is a poor match for anything that needs structural resistance or a neutral background, where the sweetness and softness get in the way. Sliced thick and griddled it firms and caramelizes, moving toward French toast territory and a warm sandwich rather than a cold one. The assembled sandwich on this bread is documented in its own article as a build; this entry is specifically about the loaf and what makes it a particular, opinionated choice of base. On its own terms, challah is a bread that picks its company: matched carefully it makes a soft, generous sandwich, and used carelessly it overwhelms whatever it is asked to carry.