Slice the flank steak very thinly against the grain. For easier slicing, place the steak in the freezer for 15-20 minutes until firm but not frozen solid.

In a medium bowl, combine the sliced beef with 1 tbsp soy sauce, 1 tsp cornstarch, Shaoxing wine, and white pepper. Toss to coat evenly and set aside to marinate for at least 10 minutes while you prepare the other ingredients.

In a small bowl or liquid measuring cup, whisk together all the stir-fry sauce ingredients: beef broth, 1/4 cup soy sauce, oyster sauce, brown sugar, sesame oil, and 1 tbsp cornstarch. Whisk until the cornstarch is fully dissolved. Set aside.

Bring a medium pot of water to a boil. Prepare a bowl of ice water on the side. Add the broccoli florets to the boiling water and cook for 60-90 seconds, until bright green and slightly tender. Do not overcook.

Immediately use a slotted spoon to transfer the broccoli to the ice water bath. This stops the cooking process and keeps it crisp. After a minute, drain the broccoli well and set aside.

Heat 1 tablespoon of oil in a wok or large skillet over high heat until it just begins to smoke. Add half of the marinated beef in a single layer. Cook for 1-2 minutes per side, until browned and cooked through. Do not overcrowd the pan. Remove the cooked beef to a plate and repeat with the remaining beef.

Reduce the heat to medium-high. Add the remaining 1 tablespoon of oil to the wok. Add the minced garlic and grated ginger and stir-fry for about 30 seconds until fragrant.

Add the blanched broccoli to the wok and stir-fry for 1 minute to heat it through.

Return the cooked beef to the wok. Give the stir-fry sauce a quick whisk again and pour it all over the beef and broccoli.

Cook, stirring constantly, for 1-2 minutes until the sauce has thickened and coats everything beautifully. Remove from heat immediately to prevent the beef from overcooking.

Serve immediately over hot rice, garnished with toasted sesame seeds if desired.