In the basement kitchens of Bao London, a squeezed, industrious inversion of the calm, wood-panelled room upstairs, dough is being kneaded to make soft, milky bao buns, ready to be steamed on fragrant bamboo trays.

These staples of Taiwanese food, like everything else at Bao, have been subject to so much research and development that the end recipe is seen as proprietary: “Most other people buy them in but we make ours,” says Erchen Chang, one of the restaurant’s three partners. “We can’t show you how to make them,” she laughs. The hot chilli sauce is even more closely guarded – Chang, her husband Shing Tat Chung and his sister Wai Ting come in on their days off to make it in secret.

The siblings, who grew up above their parents’ restaurant in Nottinghamshire, started a stall with Chang on Netil Market, east London, two years ago, selling filled bao buns and fried chicken. “The chicken is marinated in soya milk and spices overnight. We have a huge Excel chart [showing] different variations on how the chicken comes out – the temperature, how much milk, how long we fry it,” Shing says.