1 tbsp chinkiang black rice vinegar or balsamic vinegar
3 tbsp soft brown sugar
Mix the sauce ingredients in a jug with 300ml water, whisking well to dissolve the sugar. Pour into a small pan, then simmer over a medium-high heat until reduced by half.
Put the fish in a bowl with the shaoxing rice wine or sherry. Set aside for a few minutes.
Drain the fish, then season with a pinch each of salt and ground white pepper. Heat the rapeseed oil in a wok over a high heat. Put the potato flour on a large plate, then coat the fish pieces in the flour. Carefully drop the coated fish into the oil and fry for a few minutes until the flesh has turned an opaque white colour.
Meanwhile, strain the sauce into a separate small pan and bring back to a simmer, but don’t discard what’s left in the sieve.
Warm a serving bowl and gently transfer the fish to it. Pour over the hot strained sauce, then sprinkle over some of the remaining spices from the sieve. Serve topped with shiso leaves or herbs, with rice and pak choi alongside.