In a medium bowl, combine the sliced flank steak, cornstarch, 1 tbsp soy sauce, and sesame oil. Toss to coat evenly. Let it marinate for at least 10 minutes.

In a separate small bowl, whisk together the beef broth, 1/4 cup soy sauce, oyster sauce, brown sugar, grated ginger, and minced garlic. Set aside.

Bring a pot of water to a boil. Blanch the broccoli florets for 60-90 seconds. Drain immediately and rinse with cold water to stop the cooking.

Heat 1 tbsp of oil in a large wok or skillet over high heat until shimmering. Add the beef in a single layer (cook in batches if needed) and sear for 1-2 minutes per side until browned. Remove beef from the skillet and set aside.

Pour the prepared sauce mixture into the hot skillet. Bring to a simmer, stirring constantly, until the sauce thickens slightly, about 2-3 minutes.

Return the cooked beef and blanched broccoli to the skillet. Stir to combine and coat everything in the sauce. Cook for 1 minute more until heated through. Serve immediately over rice.