Slice flank steak into three pieces along the grain. Then slice each piece against the grain into ¼" / .5cm strips.

In a bowl, combine sliced beef with soy sauce, sesame oil, Shaoxing, baking soda, 10g/1T cornstarch, and MSG. Toss to coat then marinate for 10-15 minutes.

Place about 1.5c cornstarch in a medium bowl. Toss marinated beef strips in cornstarch, ensuring each piece is lightly coated.

Shake off excess using a colander or salad spinner. Let coated beef sit for 10 minutes to hydrate.

Grate or mince ginger and mince garlic. Keep separate.

Slice scallions, separating whites and greens. Thinly slice whites. Cut green tops into 2"/5cm pieces.

Slice bell peppers into ¼" strips.

In a bowl, mix brown sugar, soy sauce, beef stock, and 5g cornstarch. Stir until cornstarch is dissolved.

Heat peanut oil in a wok or saucepan over medium heat to 375-400°F (190-205°C).

Fry beef in 3 batches, cooking for 2-3 minutes per batch until crispy. Avoid touching beef during frying. Transfer to a paper towel-lined tray.

Remove the oil from the wok and wipe out any leftover solids with paper towels. Reheat wok over high heat until water sizzles upon contact.

Add a generous drizzle of peanut oil and dried chilies. Fry for 30 seconds.

Add scallion whites. Toss. Add ginger and garlic. Stir-fry for 1 minute, stirring constantly. Lower heat if necessary to be sure ginger and garlic don't burn.

Add bell peppers and stir-fry for 90 seconds.

Pour in the sauce around the edge of the wok and bring to a simmer, cooking for 60-90 seconds until slightly thickened.

Add crispy beef to the wok and toss to coat with sauce. Add scallion greens and fold in.