Cut the beef into thin slices.
For the marinade, mix the soy sauce, sesame oil, sherry and cornflour together in a bowl. Add the beef, spoon over the marinade and leave to marinate for a few minutes.
To cook the beef, heat the vegetable or groundnut oil in a wok until it's very hot. Add the beef and the marinade and stir fry for about one minute.
Carefully pour the stir-fried beef into a sieve set over a bowl to strain off the excess juices. Discard the juices and set aside the beef until ready to serve.
For the noodles, wipe the inside of the wok clean with kitchen towel and return the wok to the heat.
Add the vegetable or groundnut oil to the wok. Heat until very hot, then add the onion, garlic, ginger and chilli and stir fry for 1-2 minutes.
Add the red pepper and most of the sherry. Cook for 1-2 minutes then add the mangetout and stir fry for another minute.
Add the noodles and pesto and stir until thoroughly mixed and heated through. Add a pinch of sugar and the remaining sherry.
Add the spring onions and drizzle over the sesame oil.
Return the beef to the wok, mix with the other ingredients and stir fry for another minute until thoroughly reheated. Season with plenty of freshly ground black pepper.
To serve, divide between two plates and sprinkle with coriander.