In a medium bowl, combine the sliced flank steak with soy sauce and cornstarch. Let it marinate for at least 15 minutes while you prepare other ingredients.

Heat vegetable oil in a large skillet or wok over medium-high heat. Add the marinated beef and stir-fry until browned, then remove from the skillet and set aside.

Add a little more vegetable oil if needed, then add the broccoli florets and stir-fry for 3-5 minutes until crisp-tender.

Add the minced garlic and grated ginger to the skillet and stir-fry for 30 seconds until fragrant.

In a small bowl, whisk together the beef broth, soy sauce, oyster sauce, brown sugar, and cornstarch for the sauce.

Pour the sauce into the skillet with the broccoli, garlic, and ginger. Bring to a simmer and cook until the sauce thickens.

Return the cooked beef to the skillet and toss to coat evenly with the sauce. Stir in the sesame oil and serve immediately with rice.