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1
Cut the flank steak with the grain into 2- to 3-inch-wide strips, then cut each strip against the grain into 1/4-inch-thick pieces.
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2
Place the beef and the remaining ingredients in a medium bowl and stir to evenly coat the meat; set aside.
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3
Place the Shaoxing or sherry, soy sauce, cornstarch, brown sugar, and vinegar in a small bowl and stir to combine; set aside.
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4
Heat a 14-inch flat-bottomed wok over high heat until a bead of water vaporizes when dropped in the pan.
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5
Drizzle 1 tablespoon of the oil around the perimeter of the wok and add the reserved beef in an even layer.
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6
Cook undisturbed until the beef begins to sear, about 1 minute.
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7
Using a metal spatula, stir-fry for 30 seconds until the beef is lightly browned but not cooked through.
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8
Transfer to a large plate.
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9
Drizzle 1 teaspoon of the oil around the perimeter of the wok.
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10
Spread half of the mushrooms around the perimeter of the wok and season lightly with salt and pepper.
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11
Sear, stirring once halfway through the cooking time, until golden brown, about 2 minutes.
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12
Continue to stir-fry until the mushrooms are tender, about 30 seconds to 1 minute more.
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13
Transfer the mushrooms to the plate with the beef.
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14
Repeat with another teaspoon of the oil and the remaining mushrooms.
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15
Drizzle the remaining teaspoon of oil around the perimeter of the wok and add the leeks, celery, and garlic.
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16
Stir-fry until the leeks are wilted, about 2 minutes.
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17
Return the beef, mushrooms, and any accumulated juices from the plate to the wok.
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18
Stir the reserved soy saucecornstarch mixture and add it to the wok.
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19
Stir-fry until the beef is just cooked, about 30 to 60 seconds.
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20
Serve immediately with steamed rice.
