Bōluó Bāo (菠萝包) is the pineapple bun, a soft sweet roll capped with a crackly sugar-cookie crust whose crazed golden pattern resembles a pineapple skin, though there is no pineapple in it at all. The angle is a two-dough contrast baked into one object. A light, slightly sweet leavened bun carries a separate sugary paste topping that crisps and fractures in the oven, so the whole appeal turns on the meeting of a tender crumb below and a thin shattering shell on top. The most common sandwich form splits the bun and slides in a cold slab of butter, the bōluó yáu, where the heat of a fresh bun softens the butter into the crumb.
The build is two preparations finished together. The base is a milk-enriched yeast dough, proofed until light and shaped into rounds. The crust is a stiff paste of sugar, fat, flour, and egg, worked smooth and chilled, then pressed or draped in a thin sheet over each proofed bun before baking; as the bun rises and the oven heat hits the sugar, the topping spreads, dries, and cracks into the characteristic web. Good execution shows a bun that is soft and faintly sweet with an even crumb, and a topping that is crisp and sandy, audibly crackly, evenly browned, and bonded to the dome rather than sliding off. The failure modes are specific: too little proof and the bun bakes up dense and tight under a topping that never gets to crack properly; a topping mixed too soft or laid too thick runs down the sides into a chewy puddle instead of setting into a shell; over-baked, the crust scorches bitter and the crumb dries out. For the buttered version, the bun has to be warm and the butter cold and thick, so it half-melts rather than either staying a hard cold block or vanishing entirely.
It shifts mostly by what is added at the split and by tweaks to the topping. Beyond the cold-butter classic, the bun is filled with custard, red bean, shredded coconut, or a savory shredded pork, and some bakeries scent the crust with a little extra vanilla or work in a custard core. The cocktail bun and other sweet enriched rolls of the same cha chaan teng tradition share the soft-dough logic but carry their own fillings and shapes, and those are separate preparations rather than crowded in here. What keeps bōluó bāo itself is the pairing that gives it its name: a soft leavened bun under a thin, crazed, sugary crust, with no pineapple anywhere in sight.