Běijīng Kǎoyā Juǎn (北京烤鸭卷) is the Peking duck wrap, the table-assembled roll of roast duck skin and meat with scallion, cucumber, and sweet bean sauce folded into a thin wheat pancake. The angle is contrast and restraint inside one small parcel. The whole construction exists to frame crisp, fatty roast duck skin: the soft bǎobǐng wrapper, the sharp raw scallion, the cool cucumber, and the dark sweet tiánmiànjiàng are each there to set off the duck rather than crowd it. Get the proportions right and a single roll carries crackling skin, a slick of sauce, and a clean vegetal cut in every bite; get them wrong and it is either greasy and flat or so loaded the duck disappears.
The build runs in a fixed order and is done by hand at the table. A thin, pale wheat pancake is laid flat and a little sweet bean sauce is brushed across it, kept to a film so it seasons without drowning the wrap. A piece or two of roast duck goes on next, the prize being skin with a thin layer of fat and meat carved so it stays crisp; then a few batons of raw scallion and cucumber are laid in a line, not a heap. The wrapper is folded over one end and rolled tight so it holds without bursting. Good execution shows the skin still audibly crisp, the sauce present but not pooling, the scallion sharp and the cucumber cool, all bound in a wrapper soft enough to roll without cracking. The failure modes are specific: a cold or stiff pancake splits at the seam and the roll falls apart, too much sauce turns the wrapper to paste and mutes everything, duck carved and left to sit goes from crisp to chewy and damp, and an overstuffed roll cannot be closed or eaten in hand.
It shifts mostly by what goes alongside the duck and how the duck itself is presented. Some kitchens add a little sugar or a sprinkle of fine sugar with the skin for a sweeter first bite, others offer pickled vegetables or a sharper sauce; a few serve the skin separately from the meat so the textures stay distinct. The wrapper can be swapped for a small steamed lotus-leaf bun for a softer, breadier version, a different vehicle for the same filling. Where the pancake itself is the subject, that thin pliable round, the bǎobǐng, is its own preparation and deserves its own article rather than being crowded in here. What anchors the wrap is the order of assembly and the proportion: duck first in importance, everything else in service of it.