Slice flank steak against the grain into thin strips. Combine with baking soda, Shaoxing wine, light soy sauce, oyster sauce, white pepper, water, and cornstarch. Marinate for at least 15 minutes.

In a bowl, whisk together oyster sauce, light soy sauce, dark soy sauce, Shaoxing wine, sugar, chicken broth, and cornstarch to create the stir-fry sauce. Set aside.

Boil salted water in a saucepan, add broccoli florets, blanch for 1-2 minutes, then transfer to an ice bath. Set aside.

Heat cooking oil in a hot wok, add marinated beef in a single layer. Sear for about 30 seconds on each side until browned. Remove and set aside.

In the wok, add more oil and sauté minced garlic and ginger for about 30 seconds. Toss in blanched broccoli, stir-fry for 1 minute.

Add cooked beef and stir-fry sauce back into the wok, stir quickly to coat everything, and cook for 1-2 minutes until the sauce thickens.

Drizzle toasted sesame oil over the dish and serve immediately, garnished with green onions. Enjoy with steamed rice or noodles.