Combine the sliced beef with the marinade ingredients (neutral oil, Shaoxing wine, light soy sauce, cornstarch, water, and baking soda). Marinate for 1 hour.

In a small bowl, mix the sauce by dissolving the brown sugar in the hot water or stock, and then stir in the light and dark soy sauces.

Dredge the marinated beef slices in the cornstarch until thoroughly coated.

Heat 2/3 cup neutral oil in a wok over high heat. Spread the flank steak pieces evenly in the wok and sear for 1 minute on each side until crispy. Transfer the beef to a plate.

Drain the oil from the wok, leaving 1 tablespoon behind. Turn the heat to medium-high. Add the ginger and dried chili peppers. After about 15 seconds, add the garlic and white parts of the scallions. Stir for another 15 seconds and add the premixed sauce.

Let the sauce simmer for about 2 minutes, and slowly stir in the cornstarch slurry mixture. Cook until the sauce has thickened enough to coat the back of a spoon.

Add the beef and green parts of the scallions, and toss everything together for another 30 seconds. Serve with steamed rice.