How to Make It
In a shallow bowl, dust the flank steak pieces with the baking soda and toss gently. Refrigerate for 30 minutes.
In a small bowl, combine the soy sauce, sake, oyster sauce, Worcestershire, sugar and sesame oil and whisk to blend. In another small bowl, whisk 1/2 cup of the chicken stock with 2 teaspoons of the cornstarch.
In a wok, heat 2 tablespoons of the canola oil until shimmering. Add the broccoli and stir-fry over high heat until the florets are starting to brown, about 5 minutes. Add the remaining 1/2 cup of chicken stock and cook until the stock has evaporated and the broccoli is crisp-tender, about 3 minutes. Transfer the broccoli to a bowl.
Heat another 2 tablespoons of oil in the wok. Add the onion and cook over moderately high heat until browned and beginning to soften. Scrape the onion over the broccoli. Wipe out the wok.
Heat the remaining 2 tablespoons of oil in the wok. Toss the meat with the remaining 1 teaspoon of cornstarch. Add the garlic and ginger to the wok and stir-fry until light brown and fragrant, about 30 seconds. Add the meat and stir-fry until no longer pink, about 2 minutes. Return the broccoli and onion to the wok and toss to combine. Add the soy sauce mixture and stir-fry until the meat is cooked through and the sauce is hot, about 2 minutes. Stir the chicken stock-cornstarch mixture and add it to the wok. Bring to a boil and, when the sauce thickens, season with salt and serve immediately.