Velvet the Beef: In a medium bowl, toss the thinly sliced beef with the bicarbonate of soda until it's evenly coated. Set aside for 15 minutes. Rinse the beef thoroughly under cold water to remove the bicarb, then pat it extremely dry with kitchen paper. In a clean bowl, mix the cornflour, light soy sauce, Shaoxing wine substitute, and sesame oil until you have a smooth, milky-looking paste. Add the beef and toss well to coat. You should see a thin, glossy film clinging to each piece. Leave to marinate for 10 minutes while you prepare the other ingredients.

Blanch the Broccoli: Bring a large pot of salted water to a vigorous, rolling boil. Drop in the broccoli florets and cook for exactly 60 seconds. As soon as the water returns to a boil and the broccoli turns a vivid, bright green, drain it immediately and plunge it into a bowl of iced water. This stops the cooking process and sets the colour. When cool, drain it thoroughly and set aside.

Mix the Sauce: In a small bowl, whisk together the oyster sauce, dark soy sauce, light brown sugar, and beef stock. Stir until the sugar has completely dissolved. You should have a dark, glossy, aromatic liquid. Set this near your stove.

The First Sear: Place your wok over a high heat and add 1 tablespoon of the vegetable oil. Wait until you see a faint wisp of smoke rising from the oil—this is your cue that it's hot enough. Add half the beef in a single layer. Don't overcrowd the wok. Let it sear undisturbed for 45 seconds. You will hear a powerful, satisfying sizzle. The edges of the beef will turn a deep golden brown. Flip the pieces and cook for another 30 seconds. The beef should be browned on the outside but still tender. Transfer to a clean plate. Repeat with the remaining oil and the rest of the beef.

Aromatics and Broccoli: Reduce the heat to medium. Add the remaining tablespoon of oil to the wok. Tip in the minced garlic and grated ginger. Stir-fry for just 15 seconds, until they become incredibly fragrant and the garlic just begins to turn a pale gold at the edges. Be careful not to burn it. Immediately add the blanched broccoli florets. Toss them in the aromatic oil for about 30 seconds, until they are lightly coated and warmed through.

Bring It All Together: Return the seared beef and any accumulated juices to the wok. Give the sauce a quick stir and pour it in around the edges. Turn the heat back up to high. As the sauce begins to bubble and thicken—you'll see it turn from a watery liquid into a glossy, sticky glaze—toss everything continuously for about 1 minute. The sauce should coat the beef and broccoli beautifully, leaving very little liquid in the bottom of the wok.

Finish and Serve: Remove the wok from the heat immediately. The smell in your kitchen should be a heady mix of caramelised soy, garlic, and sesame. Transfer the stir-fry to a warm serving platter. Scatter over the toasted sesame seeds and sliced spring onions. Serve at once, while it's still steaming and the sauce is at its most luscious.