1.25 pounds flank steak – thinly sliced against the grain
1 tablespoon light soy sauce
1 tablespoon Shaoxing wine
12 ounces bell peppers – cored and thinly sliced
8 ounces yellow onion – thinly sliced
1 tablespoon garlic – finely minced
1 tablespoon fresh ginger – finely minced
0.5 cup beef stock
2 tablespoons oyster sauce
1 teaspoon dark soy sauce
1 tablespoon sugar
2 teaspoons cornstarch
0.5 teaspoon freshly ground black pepper
2 tablespoons neutral oil
0.5 cup scallions – cut into 1-inch pieces
1 teaspoon sesame oil
Instructions
Partially freeze the flank steak for 20 minutes to firm it up, then slice thinly against the grain.
In a bowl, toss the sliced beef with the light soy sauce and Shaoxing wine until coated; let marinate 15 minutes while you prep the vegetables.
In a separate bowl, whisk together the beef stock, oyster sauce, dark soy sauce, sugar, cornstarch, and freshly ground black pepper until smooth; set the sauce aside.
Heat a wok or large skillet over high heat until very hot, 2–3 minutes. Add the neutral oil, swirl to coat, and when it just begins to smoke, add half the beef in an even layer.
Sear the beef without moving for 30 seconds, then stir-fry until just browned but still a touch pink, 1–2 minutes more. Transfer to a plate and repeat with the remaining beef.
Return the wok to high heat. Add the bell peppers and yellow onion and stir-fry until crisp-tender with light char at the edges, 2–3 minutes.
Add the garlic and fresh ginger and stir-fry until fragrant, about 30 seconds.
Stir the sauce, then pour it into the wok. Bring to a vigorous simmer, tossing constantly, until glossy and thickened, 1–2 minutes.
Return the beef and any juices to the wok, add the scallions and sesame oil, and toss until the beef is just heated through and the scallions are bright green, 30–60 seconds.