Place your 1 ½ lb flank steak sliced thinly against the grain in the freezer for 15 minutes — this firms it up and makes it much easier to slice thinly. Once chilled, slice against the grain into strips about 1/4 inch thick.

In a mixing bowl, combine the 3 tbsp soy sauce, 1 tbsp cornstarch, 1 tsp sesame oil, and 1 tsp baking soda the secret to restaurant-tender beef. Add the sliced flank steak sliced thinly against the grain and toss well to coat. Let marinate for at least 15 minutes at room temperature (or up to 1 hour in the fridge).

In a small mixing bowl or measuring cups, whisk together the ½ cup low-sodium beef broth, ⅓ cup oyster sauce, 3 tbsp soy sauce, 2 tbsp brown sugar, 1 tbsp cornstarch, and 1 tsp sesame oil until smooth and the 1 tbsp cornstarch is fully dissolved. Set aside.

Heat your wok or large skillet over high heat until very hot — almost smoking. Add 1 tablespoon of vegetable oil. Add the 1 lb broccoli cut into bite-sized florets florets and stir-fry for 1 minute. Add the ¼ cup water for steaming the broccoli, cover with a lid or aluminum foil, and let steam for 2 minutes until the 1 lb broccoli cut into bite-sized florets is bright green and just tender-crisp. Transfer the 1 lb broccoli cut into bite-sized florets to a plate and set aside.

Return the wok to high heat and add the remaining 2 tablespoons of vegetable oil. Once shimmering, add the marinated 1 ½ lb flank steak sliced thinly against the grain in a single layer (work in two batches if needed to avoid crowding). Sear without stirring for 60 seconds, then stir-fry for another 1–2 minutes until just cooked through and lightly browned. Transfer the 1 ½ lb flank steak sliced thinly against the grain to the plate with the 1 lb broccoli cut into bite-sized florets.

Reduce the heat to medium. Add a small splash of vegetable oil if the wok looks dry, then add the 4 cloves garlic minced and 1 tbsp fresh ginger grated. Stir-fry for 30 seconds until fragrant — don't let it burn.

Give the sauce a quick re-whisk (the 1 tbsp cornstarch settles), then pour it into the wok. Stir and let it come to a simmer — it will thicken quickly, in about 1–2 minutes.

Return the 1 ½ lb flank steak sliced thinly against the grain and 1 lb broccoli cut into bite-sized florets to the wok. Toss everything together until well coated in the glossy sauce and heated through, about 1 minute. Taste and adjust seasoning — add a pinch of brown sugar if you want it sweeter, or a splash of soy sauce for more saltiness.

Serve immediately over steamed white rice. Garnish with 1 tsp sesame seeds and sliced stalks green onions thinly sliced if desired.