To make the marinade, in a large bowl, whisk together the cornstarch, tablespoon of oil, soy sauce, and baking soda. Add the steak and toss to coat.
Marinate for at least 10 minutes, and up to 30 minutes. There’s no need to refrigerate the steak.
To make the stir fry sauce, in a small bowl, whisk together the broth (or water), soy sauce, brown sugar, Shaoxing wine (or more broth), cornstarch, sesame oil, ginger, and garlic. Set aside.
Blanch the broccoli in a large pot of boiling water for 1 minute. Drain and set aside. Alternatively, you can sauté the broccoli in 1 tablespoon of olive oil for 5 to 7 minutes, until crisp-tender. Set aside.
Heat the olive oil in a large skillet over high heat. Working in batches to prevent crowding the pan, add the beef, in a single layer, and cook for 1 to 2 minutes per side, until browned and almost cooked through (test a piece if you’re unsure).
If you’re working in batches, transfer the steak to a plate and return all steak to the pan once cooked. Whisk the stir fry sauce again to make sure the cornstarch isn’t stuck to the bottom of the bowl, then add the sauce to the pan.
Reduce the heat to medium-low and simmer for 2 to 3 minutes, until the sauce thickens. Fold in the broccoli and cook for 1 minute to heat through. If desired, add 1 to 2 tablespoons of water to thin the sauce.
Season to taste with salt and pepper.
Garnish with toasted sesame seeds and top with green onions (if using). Serve over rice or Asian noodles if desired.