A sublime secret is hidden away, discovered only if you ring a doorbell beside a green door in a brick wall. You’ll pass through the grassy yard of an 1880s school, and in the old bike shed, join a daytime garden party. The changing menu is rigorously British and fresh, yet without flourish: green pea soup, roast sirloin, leek and wigmore tart, fish and chips, loose-leaf tea. Your companions will be high-functioning artists, designers, and professionals, many of whom now lease space in the former school, plus the occasional kid, if they behave as well as a Victorian child. In fine weather, it’s easier to find a seat because dining spills outdoors, the better to enjoy jugs of rhubarb and ginger fizz.