Prepare the Beef: Begin by slicing your beef against the grain into thin, bite-sized strips, aiming for pieces about 0.5cm thick. Place the sliced beef in a medium bowl, sprinkle over 60g of cornflour, and toss thoroughly until every piece of beef is lightly coated and looks pale and powdery. Set aside to marinate for at least 30 minutes at room temperature – this coating will create a beautifully crisp exterior and help thicken the sauce later.

Make the Sauce Base: While the beef marinates, prepare the sauce. In a separate bowl, whisk together the soy sauce, 120ml water or beef stock, light brown sugar, rice vinegar, sesame oil, and optional chilli flakes. Stir until the sugar is fully dissolved and the mixture is a uniform brown liquid, smelling faintly sweet and savoury. Set this aside.

Sauté the Aromatics: Heat 2 tablespoons of vegetable oil in a large frying pan or wok over medium-high heat until it shimmers. Add the thinly sliced onion and cook for 3-4 minutes, stirring occasionally, until the slices soften and become translucent, releasing a sweet, pungent aroma. Add the minced garlic and grated ginger, cooking for another minute until fragrant, being careful not to let them brown too much, as they will smell slightly toasted.

Cook the Beef (in Batches): Remove the cooked aromatics from the pan and set them aside. Add the remaining vegetable oil to the pan and increase the heat to high. Once the oil is very hot and shimmering, add about a third of the cornflour-coated beef in a single layer. You should hear a distinct sizzling sound immediately. Cook for 2-3 minutes per side, turning once, until the beef is deeply browned and crispy on the edges, turning a rich, caramelised brown colour. Do not overcrowd the pan, or the beef will steam instead of fry. Repeat with the remaining beef in two more batches, ensuring each batch achieves that lovely golden-brown crust.

Combine and Thicken the Sauce: Once all the beef is cooked, return the aromatics and all the cooked beef to the pan. Pour the prepared sauce mixture over the beef and onions. Bring the sauce to a boil, stirring gently. As it heats, you’ll notice the sauce starting to thicken and become glossy, transforming into a beautiful rich, dark brown glaze that clings to the beef, usually within 2-3 minutes. It should coat the back of a spoon.

Finish and Serve: Once the sauce has thickened to your desired consistency, remove the pan from the heat. Give it a final stir to ensure everything is evenly coated. Garnish generously with freshly sliced spring onions, which will add a lovely vibrant green colour and a fresh, mild oniony bite. Serve immediately while hot.