Fàntuán with Ròusōng (饭团肉松) is a glutinous rice roll built around pork floss, the cold or warm sticky-rice cylinder that carries dried, fluffy meat as its anchor. The angle here is contrast of texture and density: the rice is dense, chewy, and barely seasoned, and the ròusōng is airy, sweet-savory, and almost weightless, so the whole thing works by setting a heavy starch frame against a light, intensely flavored core. Get the ratio right and each bite reads as rice with a clean savory thread running through it; get it wrong and the floss either disappears into the mass or sits in a dry clump that the rice cannot carry.
The build is simple and depends almost entirely on the rice and the pack. Glutinous rice is steamed until tender and tacky, then spread out on a cloth or sheet of plastic while still warm. The ròusōng goes down the center in a generous line, and the rice is rolled tightly around it into a firm cylinder, compressed so it holds together when cut or eaten by hand. Good execution shows in the structure holding: the rice is warm enough to be pliant and cool enough not to steam the floss into a paste, the roll is packed tight so it does not crumble, and the floss is dry and fresh so it keeps its fibrous lift rather than turning gummy. Sloppy versions fail in obvious ways. Rice rolled when too hot wilts the floss and turns the center damp and matted; rice that has gone cold and stiff before rolling cracks apart and sheds at the first bite; too little floss leaves long stretches of plain starch with nothing happening, and too much packs the core into a dense, oversweet wad.
It shifts mostly by what shares the roll with the floss. The plainest form is ròusōng alone, and that is the version most stalls are judged on. A length of yóutiáo, fried dough stick, is the most common addition, tucked in for crunch against the soft rice. Pickled mustard greens or suāncài are folded in for acid and bite, cutting the sweetness of the floss. A smear of sweetened condensed milk or a scatter of sugar pushes some versions toward breakfast-sweet. The fish-floss variant, made with yúsōng instead of pork, is a close relative built on the same logic but with its own flavor and is better treated on its own terms than folded in here. The same is true of the savory egg and pickle builds, which become a different sandwich once the floss is no longer the lead.