Marinate the beef: In a medium bowl, combine the thinly sliced beef with salt (if using), cooking wine, oyster sauce, water or chicken stock, and white pepper. Mix thoroughly. Add the cornstarch and vegetable oil, ensuring the beef is well-coated. Let the beef marinate for at least 15 minutes while you prepare the other ingredients.

Prepare the vegetables: Slice the ginger and garlic, remove the roots from the shiitake mushrooms and slice them, and cut the scallions into sections, separating the white and green parts.

Cook the beef: Heat a tablespoon of cooking oil in a wok or large skillet over medium-high heat. Once hot, add the marinated beef in a single layer. Stir-fry for 1-2 minutes until the beef is browned on the outside but still tender. Remove the beef from the wok and set aside.

Stir fry the aromatics and vegetables: In the same wok, add another tablespoon of oil if needed. Add the sliced ginger and garlic, stir-frying for 30 seconds until fragrant. Add the white parts of the scallions and the sliced shiitake mushrooms. Stir-fry for 2-3 minutes until the mushrooms are tender and lightly browned.

Combine and season: Return the cooked beef to the wok, mixing it with the mushrooms and aromatics. Stir in the remaining oyster sauce, light soy sauce, and sesame oil (if using). Toss everything together, allowing the sauce to coat the beef and mushrooms. Stir-fry for another 1-2 minutes to combine the flavors.

Finish and serve: Turn off the heat and stir in the green parts of the scallions. Serve the beef and mushroom stir fry hot over rice or noodles, garnished with additional scallions if desired.