Put the beef in a large bowl and toss with the cornflour and 1/2 tsp each of salt and ground black pepper. Heat the oil in a large frying pan or wok over a medium heat and fry the beef until crispy. Remove from the pan and set aside (you don’t have to remove it from the pan, this but it ensures the beef doesn’t overcook and stays as crispy as possible). Reserve the oil in the pan.

Stir in the onion and red pepper and fry for a few minutes until softened, then add the spring onions, chilli, garlic and ginger and cook for a couple of minutes longer before adding the chilli sauce, ketchup, vinegar and soy sauce. Mix everything together, cooking for 1 minute, then mix in the noodles and crispy beef. Cook for 2 mins, then serve in bowls with a scattering of sesame seeds, if you like.