Begin by thinly slicing the sirloin steak against the grain, which enhances tenderness. In a mixing bowl, sprinkle the sliced beef with salt and freshly ground black pepper, tossing gently to ensure an even coat. Allow the seasoned meat to rest for about 10 minutes while you heat up your wok.

Heat a tablespoon of sunflower oil and half a tablespoon of sesame oil in your wok over medium-high heat. Once the oil is shimmering and hot, add the seasoned beef in a single layer. Stir-fry for approximately 2-3 minutes until the beef is just browned and slightly crispy on the edges. Remove the beef from the wok and set aside, ensuring it remains warm.

In the same hot wok, add another tablespoon of oil if necessary, then toss in sliced bell peppers and onions. Stir-fry the vegetables for about 2-3 minutes until they begin to soften and the colors brighten. Stir continuously to maintain their crunch, allowing them to absorb any lingering beef flavors left in the pan.

In a mixing jug, whisk together cornflour, soy sauce, oyster sauce, rice wine, and half a cup of beef stock until smooth. This mixture will create a glossy and flavorful sauce for your Black Pepper Beef stir-fry. Set it aside, ready to enhance the dish.

Add minced garlic and grated ginger to the sautéed vegetables in the wok, stirring for about 30 seconds until fragrant. Pour in the sauce mixture, allowing it to bubble and thicken slightly. Return the cooked beef to the wok, stirring to coat the meat and vegetables evenly in the savory sauce.

Allow the Black Pepper Beef to simmer together for another 2-3 minutes, blending all the flavors nicely. The sauce should thicken and cling to the ingredients, promising a rich flavor. Frequently stir while simmering, checking for a glossy finish that indicates it’s ready to serve.