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Stir together soy sauce, vinegar, oyster sauce, and cornstarch.
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Toss steak with 1/2 teaspoon salt and 1 teaspoon pepper.
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Heat wok over high heat. Add 2 tablespoons vegetable oil, swirling to coat, then stir-fry garlic and ginger until golden and fragrant, about 30 seconds.
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Add beef, quickly spreading pieces in 1 layer on bottom and sides of wok.
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Cook, undisturbed, 2 minutes, then stir-fry until meat is just browned but still pink in center, about 1 minute.
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Transfer to a bowl.
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Wipe wok clean, then swirl in remaining tablespoon oil and stir-fry cabbage stems over high heat until crisp-tender, about 2 minutes.
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Add cabbage leaves and beef with juices, then stir soy mixture and add. Stir-fry until sauce is simmering and slightly thickened, 1 to 2 minutes. Discard ginger if desired
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Season with salt