1tablespooncornstarch(mixed with 1 tablespoon water)
2scallions(cut into 1-inch long slices on the diagonal)
Combine the sliced beef with 1 teaspoon oil, 1 teaspoon soy sauce, and 1 tablespoon cornstarch and let it sit and marinate for an hour. The beef should still be quite moist after it has marinated. If it looks too dry, add a tablespoon of water to it.Next, dredge the marinated beef slices in the remaining 1/4 cup of cornstarch until lightly coated. These steps ensure that the Mongolian Beef is tasty and crispy!
Heat 1/3 cup vegetable oil in the wok over high heat. Just before the oil starts to smoke, spread the flank steak pieces evenly in the wok, and let sear for 1 minute (depending upon the heat of your wok). Turn over and let the other side sear for another 30 seconds. Remove to a sheet pan; tilt it slightly to let the oil drain to one side (lean it on a cookbook or cutting board). The beef should be seared with a crusty coating.
Drain the oil from the wok, leaving 1 tablespoon behind, and turn the heat to medium-high. Add the ginger and dried chili peppers, if using. After about 15 seconds, add the chopped garlic. Stir for another 10 seconds and add the 1/4 cup low sodium soy sauce and chicken stock (or water).
Bring the sauce to a simmer, add the brown sugar, and stir until dissolved.
Let the sauce simmer for about 2 minutes and slowly stir in the cornstarch slurry mixture--until the sauce coats the back of a spoon.
Add the beef and scallions and toss everything together for another 30 seconds. There should be almost no liquid, as the sauce should be clinging to the beef. If you still have sauce, increase the heat slightly and stir until thickened.