Remove any large bits of fat from the beef, then slice into very thin strips. In a mixing bowl, combine the beef strips with the soy sauce, garlic and ginger. Leave to marinate in the fridge for as long as you have time for (up to 2 hours). If you’re pushed for time, just leave at room temp as you prepare the other ingredients.
Mix 2 tbsp of the cornflour into the beef and leave for a few minutes. It’ll be fairly sticky at this point, which is fine.
Place a second bowl next to the beef and fill it with the rest of the cornflour. Mix the beaten egg into the beef, then take a strip and thoroughly coat it in the cornflour. Make sure you really press the cornflour into the beef, then give it a good shake before resting on a baking tray. Repeat with the remaining strips of beef. I know this step is tedious but it’s worth it for maximum crispiness! If you run out of cornflour, just add more as needed.
Heat 240ml/1 cup of the oil in a large, heavy-based saucepan over a medium-high heat until it reaches 180°C (356°F). When it's hot enough, a crumb should sizzle when it hits the oil. Add half the beef (or as much as will comfortably fit) and use tongs to spread it out in the pan. Leave to fry for 2 minutes to allow the batter to cling to the beef, then cook for a further 2-3 minutes, stir-frying until golden and crisp all over. Remove and place on a wire rack set over a baking tray or kitchen paper to catch any excess oil. Repeat with the second batch, then discard the oil.
Whisk all the sauce ingredients together in a small bowl until combined.
Heat the remaining oil in the pan over a medium heat. Add the onion and carrots and fry for a few minutes until they start to soften, then add the chilli and fry for a minute longer. Toss in the beef and sauce and give it a good stir until the sauce thickens and clings to the beef.
Serve with rice or noodles then tuck in and enjoy!