Kǎo Bāozi (烤包子) is the baked bun, a Xinjiang parcel of thin unleavened dough sealed around diced lamb and onion and baked hard against the wall of a clay tonur oven until the shell blisters and browns. Unlike the soft steamed bāozi of eastern China, this is a dry-baked pastry, closer in spirit to a samsa, and the difference is the whole point. The angle is the contrast between a crisp, almost cracker-like skin and a juicy, fatty filling that steams in its own sealed pocket while the outside bakes.
The build is a thin dough folded into a squared parcel around a coarse meat filling. The dough is a plain wheat-and-water mix, sometimes barely leavened, rolled thin and cut into squares rather than gathered into pleats. The filling is hand-diced lamb, not minced, mixed with diced onion in roughly equal measure, salt, cumin, black pepper, and often a piece of tail fat so the meat stays moist and rich as it cooks. A spoon of filling sits in the center of each square, the corners are folded over into a flat envelope and pressed firmly shut, and the parcels are slapped onto the inner wall of the hot clay oven where dry radiant heat sets the skin fast. Good execution shows a skin that is thin, blistered, and crisp enough to crack, seams that held so the rendered juice stayed in until the bite, lamb that is tender and clearly cumin-scented, and onion that has gone sweet and soft against the fat. The failure modes are specific: dough rolled too thick bakes into a hard, doughy slab; a poorly sealed parcel splits and bleeds its juice onto the oven wall and dries out; too lean a filling with no fat reads tight and dry; an oven too cool leaves the skin pale and tough instead of crisp.
It shifts mostly by the fat in the filling and the spicing. More tail fat gives a richer, juicier bun; leaner mixes run drier and need careful timing. Cumin and pepper are constant, but some bakers add chili or extra onion for sweetness. Beef sometimes stands in where lamb is scarce. The soft steamed lamb or pork bāozi of the eastern tradition is an entirely different preparation built on a leavened dough and a steamer, and the cumin-lamb flatbreads and skewers of the same Xinjiang kitchen each run their own logic; those deserve their own articles rather than being crowded in here. What keeps kǎo bāozi its own entry is the thin oven-baked skin sealed around hand-diced lamb and onion, crisp outside and juicy within.