In a bowl, mix together the soy sauce, cornstarch, and beef slices. Let marinate for 10 minutes.
Heat 1 tablespoon of vegetable oil in a large pan over medium-high heat. Add the beef slices and cook until browned, then remove from the pan and set aside.
In the same pan, add the remaining vegetable oil. Stir-fry the garlic and ginger until fragrant.
Add the broccoli florets and beef broth to the pan. Cover and steam for about 5 minutes, until broccoli is tender-crisp.
Return the beef to the pan. Stir in the oyster sauce, sesame oil, and sugar. Toss everything together and serve hot.
Notes
For extra flavor, garnish with toasted sesame seeds or sliced green onions before serving.