1. Prepare the Beef: Thinly slice the beef ACROSS the grain. The slices should be maximum 1/4" thick. In a medium bowl, whisk together the marinade ingredients and add in the beef slices. Set aside.
2. Prepare the Sauce: In a small bowl, whisk together all of the sauce ingredients. Set aside.
3. Partially Cook the Broccoli: In a wok or large skillet bring a cup of water to a simmer. Add in the broccoli florets, close with lid. Cook the broccoli until bright green and just about halfway-cooked through, about 1 minute. Immediately drain and set aside. Rinse with cool water to stop the cooking.
4. Sear the Beef: Return wok to stovetop and wipe very dry. Turn heat to high and when very hot, swirl in just 1 tablespoon of the cooking oil. Add in the beef slices in a single layer. Let sear, undisturbed, for 1 minute. Flip and sear the other side for 30 seconds. Immediately remove the beef to a clean plate.
5. Stir-Fry: Return wok to stove and turn heat to medium-high. When hot, swirl in the remaining cooking oil. Add in the garlic and cook for 15 seconds, until fragrant. Add in the steamed broccoli, and stir fry with the garlicky oil for just a few seconds. Add in the seared beef and then the sauce ingredients. Simmer for 30 seconds until the sauce thickens and the broccoli is cooked through.