To marinade the beef, combine the soy sauce, ginger, sesame oil, garlic, white pepper and star anise in a large non-metallic bowl. Add the beef pieces and toss thoroughly. Cover with clingfilm and leave to marinade in the fridge for at least six hours (overnight is even better).
To cook the beef, drain off all the marinade and discard. Heat four tablespoons of the vegetable oil in a large frying pan over a high heat and then add the beef in batches. As the beef browns, sprinkle it with the flour and cayenne pepper and continue to cook for another 2 minutes. Drain the beef pieces in a colander as they finish browning and then place in a heavy-based casserole.
Pour 1¼pints/1 litre of water into the casserole and then add the carrots, onion and leek. Bring to a simmer and skim off any excess fat or scum. Cover with a lid and cook over a low heat (or in a low oven) for about 1½ hours or until the beef is tender and the sauce has reduced and slightly thickened.
Strain the juices through a fine sieve and again skim off any excess fat. Pick the cooked onion, carrot and leek out of the meat and discard, then pour the strained juices back onto the meat. Season to taste, return to the heat and warm through.
Cook the noodles in a large pan of boiling water for about 5 minutes until completely soft (or according to packet instructions).Drain in a colander and toss with two teaspoons of sesame oil.
Heat the remaining vegetable oil in a wok. Tip the peppers in and stir-fry for 3-4 minutes until just tender.
To assemble the dish, first divide the cooked noodles among the serving bowls. Then add a ladle or two of the Chinese beef on top. Scatter a few cooked red peppers on top. Finally, finish with a sprinkling of freshly chopped chillies, spring onions and coriander.