Every fortnight in Walthamstow, East London, a sign with a hand-painted goldfish pointing towards a kitchen window appears on the side of a residential building: “Lucky Yu Bakery pick up”. On the other side of that window is Hai Lin Leung, a general practitioner selling Cantonese-influenced baked goods from her home – think congee sourdough, bolo bao (pineapple buns), gai mei bao (cocktail buns) and more. There is no shopfront, set opening hours or seating; yet queues regularly spill down the...