Place thinly sliced flank steak in a medium bowl. Add soy sauce, cornstarch, baking soda, and sesame oil. Toss well to coat every piece. Let the beef velvet for at least 10 minutes at room temperature (or up to 24 hours in the refrigerator, covered). This step is key to achieving restaurant-tender beef.

In a small bowl or measuring cup, whisk together the soy sauce, oyster sauce, hoisin sauce, brown sugar, cornstarch, beef broth, and sesame oil until the cornstarch is fully dissolved and the mixture is smooth. Set aside.

Bring a medium pot of salted water to a boil. Add the broccoli florets and blanch for 60 seconds. Immediately drain and transfer to a bowl of ice water to stop cooking and preserve the vibrant green color. Drain well and pat dry. (Alternatively, steam for 2 minutes until bright green and just slightly tender.)

Heat a large wok or wide skillet over the highest heat your stove allows. Add 1 tablespoon of cooking oil and heat until just smoking. Add half the marinated beef in a single layer — do not stir for the first 60 seconds to allow a sear to develop. Toss and cook for another 30-60 seconds until just cooked through. Transfer to a clean plate. Repeat with remaining oil and beef. Do not crowd the pan.

Reduce heat to medium-high. Add a small drizzle of oil if needed. Add the minced garlic and grated ginger and stir-fry for 30 seconds until fragrant — watch carefully as they can burn quickly.

Add the blanched broccoli florets to the pan and toss to coat with the aromatics for about 1 minute.

Return the seared beef to the pan. Give the sauce one more quick whisk to recombine the cornstarch, then pour it over everything in the pan. Toss and stir continuously as the sauce heats — it will bubble, thicken, and turn beautifully glossy within 60-90 seconds. Remove from heat immediately once the sauce has coated everything evenly.

Serve immediately over steamed white or brown rice. Garnish generously with sliced green onions and sesame seeds. Enjoy right away for the best texture.