Place the beef in a bowl with the soy, five-spice, rice wine, chilli and cornflour, and season with black pepper. Mix well so the beef is completely coated in the thick paste and leave to marinate for at least 10 mins but 30 mins is better.
Heat 2 tbsp of oil in a wok until very hot. Add the beef to the wok, but do not overcrowd the pan – the beef needs to be in a single layer. If necessary, cook the beef in batches. Fry the beef vigorously for about 3 mins until brown and crisp and scoop onto a plate.
When all the beef is cooked give the wok a quick wipe out. Heat the remaining oil and stir fry the peppers and broccoli for a minute then pour over the stock and add the oyster sauce. Simmer everything together for 1 min then add the beef to the wok and boil briefly to thicken the sauce then serve straight away with rice or noodles.