Begin by slicing the flank steak into thin strips and place them in a bowl. Sprinkle with baking soda, then add Shaoxing wine, light soy sauce, oyster sauce, white pepper, water, and cornstarch. Mix everything well and let it marinate for at least 15 minutes to absorb the flavors and tenderize the beef.

In a separate bowl, whisk together the oyster sauce, light soy sauce, dark soy sauce, Shaoxing wine, sugar, chicken broth, and cornstarch until smooth. Set the sauce aside for later use.

Fill a pot with water, add a pinch of salt, and bring it to a boil. Add the broccoli florets and cook for 1-2 minutes until bright green and slightly tender. Drain and set aside.

Heat 1-2 tablespoons of oil in a wok over high heat. Quickly add the marinated beef in batches, searing each side for about 30 seconds until browned. Remove the beef and let it rest.

Return the wok to the heat, add more oil if needed. Sauté minced garlic and ginger for about 30 seconds until fragrant. Toss in the blanched broccoli and stir-fry for an additional minute. Add the seared beef back along with the prepared stir-fry sauce, tossing everything for 1-2 minutes until the sauce thickens.

Drizzle with toasted sesame oil and serve hot, garnished with diced green onions and alongside steamed rice.