Start by prepping the sprouts. Trim the base of each sprout and remove any damaged outer leaves. You can cut a cross into the bottom of the sprouts so that they will cook quicker, but it’s not necessary and entirely optional.
Bring a large pan of salted water to the boil, add the sprouts and cook until just tender – the timing will depend on the size of the sprouts and whether you have cut a cross on the underside. Drain and either refresh under cold running water or plunge the sprouts into a bowl of iced water to stop them cooking further. Drain and leave to dry on a clean tea towel for a few minutes.
Heat the oil in a large frying pan over a medium–high heat and turn the extractor fan on to full speed, or open a window. Add the sprouts to the hot pan and cook, shaking the pan, until the sprouts start to take on some colour.
Add the fish sauce and continue shaking the pan for 10 seconds. Add the butter and a splash of water and shake the pan again so that the butter melts and you coat the sprouts in a beautiful, glossy glaze. Serve immediately.