Marinate the beef: In a medium bowl, combine the sliced beef with 1 tablespoon of light soy sauce and 1 tablespoon of cornflour. Use your hands to massage the mixture into the meat—you’ll feel the beef become slightly tacky as the cornflour begins to adhere. Set aside for 20 minutes at room temperature.

Make the sauce: In a small bowl, whisk together the remaining 2 tablespoons light soy sauce, dark soy sauce, rice vinegar, tomato paste, brown sugar, sesame oil, and white pepper. Stir until the sugar has dissolved completely—the sauce should look a deep, glossy mahogany. Set it near the hob.

Prepare the coating: Spread the remaining 2 tablespoons of cornflour on a large plate. Working in batches, dredge each marinated beef strip in the cornflour, pressing gently so the flour adheres. The beef should look dusted, not caked; shake off any excess. You’ll hear a faint rustle as the strips settle on the plate.

First fry: Heat 3 tablespoons of oil in a wok or large frying pan over high heat until it shimmers—you’ll see faint wisps of smoke rising. Add the beef strips in a single layer, without crowding. Fry for 2 minutes without moving them; the edges will turn a deep golden brown and you’ll hear a steady sizzle. Flip and fry for another 1 minute. Transfer the beef to a plate lined with kitchen paper. Repeat with any remaining beef.

Aromatics in hot oil: Reduce the heat to medium-high and add the remaining 1 tablespoon of oil. Tumble in the garlic, ginger, and dried chilli pieces. Stir-fry for 30 seconds—the air will fill with a sharp, fragrant steam, and the garlic will turn pale gold at the edges.

Build the sauce: Pour the prepared sauce mixture into the wok. It will bubble immediately and start to thicken. Stir continuously for about 1 minute until the sauce coats the back of a spoon and looks sticky and glossy, like a dark caramel.

Return the beef and vegetables: Tip the fried beef strips back into the wok, along with the red and green bell pepper strips. Toss everything together over high heat for 90 seconds—the peppers will soften slightly but keep a little crunch, and the beef will be fully coated in the glistening sauce.

Finish and serve: Sprinkle the spring onions over the top, give everything one final toss, then slide the beef onto a warm serving plate. The sauce should cling to the meat and peppers, not pool at the bottom. Serve immediately with steamed jasmine rice.