Place the flank steak in the freezer for 20 minutes. This firms it up just enough to slice cleanly. Once chilled, cut the steak against the grain into strips about 1/4 inch thick. Toss the strips with the cornstarch in a bowl and set aside.

In a small bowl, whisk together the oyster sauce, soy sauce, sesame oil, beef broth, sugar, and cracked black pepper. Taste it and add more pepper if you like a bigger kick. Set the sauce aside within arm's reach of the stove.

Heat a large wok or skillet over high heat until it is very hot, about 2 minutes. Add 1 tablespoon of the neutral oil and swirl to coat. Add the broccoli florets in a single layer. Cook without stirring for 90 seconds so they pick up a little char, then toss and cook 1 minute more. The broccoli should be bright green and just tender with a little bite. Transfer it to a plate.

Add the remaining 1 tablespoon of oil to the same hot pan. Add the beef strips in one layer as much as possible. Let them sear undisturbed for about 60 to 90 seconds until browned on the bottom, then toss and cook another 60 seconds. The beef is done when it is just cooked through and no longer pink. Do not overcook or it will turn tough.

Push the beef to the edges of the pan. Add the garlic and ginger to the center and stir them around for 30 seconds until fragrant. Pour the sauce over everything and toss to coat. Return the broccoli to the pan and toss again. Cook together for 1 minute until the sauce thickens and coats the beef and broccoli. Remove from heat.

Serve immediately over warm jasmine rice. Scatter sliced green onions over the top and finish with an extra pinch of cracked black pepper if you like.