Start by slicing the flank steak against the grain into thin strips, about 1/4 inch thick. In a bowl, combine the sliced beef with soy sauce, peanut oil, and cornstarch, ensuring each piece is evenly coated. Allow the beef to marinate for at least 10 minutes.

While the beef marinates, mix together the chicken stock, Shaoxing wine, soy sauce, dark soy sauce, brown sugar, and cornstarch in a separate bowl. Whisk until the cornstarch and sugar dissolve completely.

In a large skillet, bring about an inch of water to a boil. Add the broccoli florets to a steaming basket or directly into the skillet, allowing them to steam for approximately 1 minute.

In the same skillet, heat a tablespoon of peanut oil over medium-high heat until shimmering. Add the marinated beef strips in a single layer, searing them for about 2-3 minutes until browned.

In the skillet, add the minced garlic and grated ginger, stirring for about 30 seconds until fragrant.

Return the cooked beef to the skillet, followed by the steamed broccoli. Pour in the prepared sauce, stirring to combine all ingredients thoroughly. Cook on medium heat for about 1-2 minutes, or until the sauce thickens.

Immediately plate your Chinese Beef and Broccoli over steaming rice. Garnish with sesame seeds to serve hot.