This should take you no longer than fifteen minutes to prepare and get on the table.
Place the cornflour in a bowl then stir in the soy sauce, sesame oil and sherry, until smooth. Add the beef stir-fry strips, stirring to combine and set aside for 10 minutes, or up to 24 hours in the fridge covered with clingfilm.
Heat a wok over a high heat until snoking hot and then add half of the oil and swirl up the sides. Add in half the marinated beef stir-fry strips and cook for 2-3 minutes until just tender and lightly golden. Tip on to a plate and keep warm. Repeat with the remaining beef strips.
Quickly wipe out the wok with kitchen paper and add the rest of the oil. add the peppers and stir-fry for 1-2 minutes. Reserve a tablespoon of the scallions to garnish then add the balance to the wok along with the mushrooms, pak choy and ginger. Then sprinkle over a tablespoon of water and continue to stir-fry for anothe rminute until the water has evaporated and the vegetables are just tender.
Add the beef back in and stir in the black bean sauce. Once it is heated through, season to taste. Serve on warmed plates with the fine egg noodles and sprinkle on the reserved scallions.
Use any selection of vegetables you fancy for this stir-fry, depending on what is available.
Serve with fried egg noodles.