12 ounces beef flank steak
1 tbsp soy sauce
1 tbsp Chinese rice wine (shaoxing) or dry sherry
1/2 tsp freshly ground black pepper
1/2 tsp sugar
3 tbsp vegetable oil, or as needed
1 medium yellow onion (8 oz), cut in thin slivers
1 & 1/2 tbsp minced garlic
1/4 tsp salt
6 green onions, cut in 2 inch lengths, thick white ends cut in half lengthwise
1. Cut the steak across the grain in 1/8-inch thick slices, 2 to 3 inches long. In a small bowl, mix the beef with soy sauce, wine, black pepper, and sugar.
2. Set a 14-inch wok over high heat. When the pan is hot, add 1 tablespoon oil and rotate the pan to spread oil. Add the yellow onion, garlic, and salt. Stir-fry until onion is lightly browned, 1 to 2 minutes. Add the green onions and stir-fry until green onion wilts slightly, about 30 seconds. Pour into a dish.
3. Return the pan to high heat. Add 1 tablespoon oil and rotate the pan to spread oil. Add half the beef and stir-fry until browned, 1 to 2 minutes. Remove meat from pan and return the pan to high heat. When the pan is hot, using 1 tablespoon oil and remaining beef, stir-fry until beef is lightly browned, 1 to 2 minutes. Return the onions and remaining beef to the pan and stir-fry until hot, about 30 seconds. Transfer to a serving dish.