In a bowl, combine flank steak with baking soda, Shaoxing wine, light soy sauce, oyster sauce, white pepper, water, and cornstarch. Mix thoroughly and let marinate for at least 15 minutes.

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

Bring a pot of water to a boil, add salt, and cook broccoli florets for 1-2 minutes. Drain and rinse with cold water.

Heat a wok over medium-high heat, add oil, and sear marinated beef for about 30 seconds on each side. Remove from skillet.

In the same skillet, stir-fry garlic and ginger for about 30 seconds until fragrant.

Add blanched broccoli back into the skillet, sauté for 1 minute, then return beef and pour in the sauce.

Toss everything together and cook for another 1-2 minutes until the sauce thickens. Serve hot, garnished with green onions if desired.