Mántou (馒头) is the plain steamed wheat bun, no filling, and in catalog terms it sits here as the base of many Chinese sandwiches rather than as a sandwich itself. The angle is its structural job. Across a wide spread of regional eating, the mántou is the thing that gets split and loaded: a soft, leavened, near-flavorless block that supplies bulk and a tender bite while leaving the seasoning entirely to whatever goes inside. Its value is in how reliably it holds a filling and how little it gets in the way, which is why it turns up under so many different stuffings.
The build, treated as a sandwich foundation, is a split-and-fill on a steamed base. The dough is a yeasted wheat dough, mixed, proofed until light, shaped into a dome, cylinder, or square, and steamed over high heat until it sets soft, pale, and matte. To carry a filling it is sliced part or all the way through, often given a quick toast or pan-sear on the cut face so it firms enough to hold a wet or fatty load, then packed. Good execution is read first on the bun and then on the marriage. The crumb should be fine, springy, and clean-tasting, the cut face firm enough not to slump, and the bun fresh enough that it absorbs a little of the filling's moisture without disintegrating. The failure modes are specific. An under-proofed bun is dense and tight and overwhelms a delicate filling with raw dough; an over-steamed one is wet and shrunken and goes to paste the moment something warm is pressed into it; an uneven steam leaves a gummy core; a day-old, unrevived mántou is dry and crumbly and the filling has to do all the work. The point of the bun is to disappear into the structure, and any of these flaws makes it the loudest part of the bite for the wrong reasons.
It shifts mostly by shape and by what it is split to hold, and the regional range is wide. A square block gives the flattest, most sandwich-like face; a domed bun is rounder and better for a torn-and-scooped style; a sliced bun fried on the cut sides is a common base for both savory and sweet loads. Northern wheat regions lean on it as an everyday staple to pair with braised meat, eggs, or pickles, and the same neutral bun underpins very different fillings from place to place without changing character. The filled and pleated bāozi seals its filling inside and is a separate preparation, as is the steamed clamshell gua bao; both belong in their own articles rather than being folded in here. What makes mántou worth its own entry is precisely this base role: a dependable, neutral steamed bun that becomes a sandwich the moment it is split and stuffed.