1. Slice flank steak against the grain into ¼-inch thick strips. In a bowl, combine beef with 1 tablespoon soy sauce, 1 tablespoon cornstarch, baking soda, 1 tablespoon vegetable oil, and 1 teaspoon sesame oil. Mix well and let marinate for 15 minutes.

2. While beef marinates, prepare the sauce: In a small bowl, whisk together ⅓ cup soy sauce, oyster sauce, brown sugar, 1 tablespoon cornstarch, beef broth, 1 teaspoon sesame oil, and black pepper. Set aside.

3. Bring a pot of water to boil. Add broccoli florets and cook for exactly 90 seconds until bright green. Drain and rinse immediately with cold water. Set aside.

4. Heat wok or large skillet over high heat until smoking. Add 2 tablespoons vegetable oil and swirl to coat.

5. Add half the marinated beef in a single layer. Let sear undisturbed for 90 seconds, flip, and cook another 60 seconds. Transfer to a plate. Repeat with remaining beef.

6. Add remaining 1 tablespoon oil to the wok. Add minced garlic and ginger, stirring constantly for 30 seconds until fragrant.

7. Stir the sauce mixture, then pour into the wok. Bring to a bubble, stirring constantly as it thickens, about 60-90 seconds.

8. Return beef and any accumulated juices to the wok. Add blanched broccoli.

9. Toss everything together for 1-2 minutes until heated through and sauce coats everything with a glossy sheen.

10. Serve immediately over steamed rice, garnished with sliced green onions and sesame seeds.