Mix the cornflour with a little vegetable oil to a smooth paste in a bowl, then add the beef strips, turn to coat in the mixture and marinate in the fridge for 1 hour.
Heat a wok, add a little oil and stir-fry the onion, chilli, garlic and ginger until soft.
Add the ingredients for the soup base and stir-fry until evenly mixed, then add the stock and