01 - Combine flank steak slices with 1 tablespoon soy sauce, 1 teaspoon cornstarch, and 1 teaspoon sesame oil in a bowl; toss to evenly coat and set aside to marinate for 10 minutes.
02 - In a small bowl, whisk together oyster sauce, 2 tablespoons soy sauce, Shaoxing wine, sugar, 2 teaspoons cornstarch, and 1/3 cup plus 1 tablespoon water until smooth; set aside.
03 - Heat 1 tablespoon vegetable oil in a large wok or skillet over medium-high heat. Add the marinated beef in a single layer and stir-fry for 1 to 2 minutes until just browned. Remove beef and set aside.
04 - Add remaining 1 tablespoon vegetable oil to the wok; stir-fry minced garlic and grated ginger for 30 seconds until fragrant.
05 - Add broccoli florets and 2 tablespoons water; stir-fry for 2 to 3 minutes until the broccoli turns bright green and is just tender.
06 - Return the cooked beef to the wok. Pour in the prepared sauce and toss to combine thoroughly. Cook for 2 to 3 minutes until the sauce thickens and coats the beef and broccoli evenly.
07 - Serve immediately, optionally accompanied by steamed rice.