01 - Combine sliced beef with 1 tablespoon soy sauce, 1 tablespoon cornstarch, and 1 teaspoon sesame oil in a medium bowl. Let rest for 10 minutes.
02 - Whisk together soy sauce, oyster sauce, water, brown sugar, cornstarch, rice vinegar, and black pepper in a small bowl. Set aside.
03 - Boil water in a pot and blanch broccoli florets for 1 minute until bright green and crisp-tender. Drain and set aside.
04 - Heat 1 tablespoon vegetable oil in a large skillet or wok over high heat. Add marinated beef in a single layer and cook for 2 to 3 minutes until browned but not overcooked. Remove from skillet.
05 - Add remaining 1 tablespoon vegetable oil to the skillet. Stir-fry garlic and ginger for 30 seconds until fragrant.
06 - Return blanched broccoli and cooked beef to the skillet.
07 - Stir the sauce mixture, then pour over beef and broccoli. Toss and cook for 1 to 2 minutes until sauce thickens and evenly coats the ingredients.
08 - Serve hot over steamed rice or noodles.