Táng Huǒshāo (糖火烧) is the sugar fire-baked bun, a dense Beijing wheat pastry layered with a dark sweet paste of brown sugar and fermented sesame, baked until the crust sets firm and the inside stays chewy and sticky. The angle is the sugar-sesame core, not a sandwich of two slices but a bread folded around its own sweet filling so the layers and the paste bake into one piece. The whole thing hinges on the balance of that paste: enough sugar and sesame to read rich and faintly malty through every layer, restrained enough that it does not turn to molten syrup and burst the bun.
The build is a coiled, filled, baked round. A firm wheat dough is rolled out thin, spread with a paste of brown or rock sugar worked together with sesame paste, often deepened with a little fermented soybean for a savory edge, then rolled and coiled so the filling sits in thin internal sheets rather than one pocket. The coil is pressed into a thick puck and baked, traditionally in a covered oven, until the outside hardens to a deep brown shell and the sugar inside melts and resets as the bun cools. Done well it has a firm, slightly crackly crust, an interior that pulls apart in chewy layers streaked dark with sesame and sugar, and a flavor that is sweet but rounded by the toasted seed and a low savory note. Done poorly the failure modes are clear: too much sugar and it runs out and scorches black on the pan while leaving the center raw, too little and it bakes dry and bland with no contrast, an under-rested dough goes tough and brick-hard, and a coil packed too loose leaves hollow gaps where the paste pooled and burned.
It shifts mostly by the filling ratio and the bake. Some kitchens push the sesame paste for a darker, almost bitter-edged depth; others keep it sweeter and lighter. The amount of fermented soybean in the paste tunes how savory the finish reads, and the crust can be taken anywhere from a soft chew to a hard snap depending on oven heat and time. It sits in a wider family of Beijing huǒshāo baked breads, most of which run savory with meat or plain, and those are their own preparations rather than crowded in here. What fixes the sugar version as its own entry is the sweet sesame-sugar paste laminated through the dough and set by the bake into a chewy, layered pastry.