In a mixing bowl, combine the sliced flank steak, water, Shaoxing rice wine, salt, and baking soda.
Mix well, then add the cornstarch and oil. Set the beef aside to marinate for 10-15 minutes.
In a bowl, mix the soy sauce, water, sugar, cornstarch, and sesame oil until smooth. Set the sauce aside.
Boil water and blanch the broccoli florets for about 1 minute. Drain and set aside.
Heat oil in a wok or pan over medium-high heat. Add the marinated beef and cook in batches until browned. Set aside.
In the same pan, sauté garlic and ginger for 15 seconds. Add the prepared sauce and bring to a simmer until thickened.
Add the beef and broccoli to the pan, stir to coat with the sauce, and garnish with sesame seeds. Serve hot and enjoy!