Adapted from Cecilia Jennie Au-Yang's "Sautéed Beef in Black Bean Sauce" published in Chopsticks Gourmet Collection, 198 Hong Kong recipes in full colour
Chill beef in freezer for 30 minutes for easier slicing. Mix together the marinade ingredients in medium bowl. Thinly slice beef and add to marinade. Let sit at room temperature for 45 minutes to 1 hour.
Mix stir-fry sauce ingredients in an 8 oz. glass measuring cup or jar, set aside.
Heat wok over high heat and add a tablespoon cooking oil. Add beef and spread out with tongs so that each piece is touching part of the hot wok. Leave beef alone to cook for a couple minutes before you start moving things around then toss around using tongs or a wooden spatula until it is cooked to your liking, about 3 - 4 minutes. Remove beef from wok and set aside on a plate.
Add a tablespoon of oil to the hot wok then add the optional sturdy veggies (onion and/or carrot). Cook for a couple minutes to soften.
Add the ginger and garlic. Add the bok choy and green onion. Cook for a minute then add the stir-fry sauce and stir-fry until veggies are tender, another minute or two. Add back the beef and stir-fry to coat with sauce. Serve immediately over hot rice.