1 tablespoon plus ¼ cup water
¼ teaspoon baking soda
1 pound flank steak, trimmed, cut into 2- to 2 ½-inch strips with grain, each strip cut crosswise against grain into ¼-inch-thick slices
3 tablespoons soy sauce
3 tablespoons dry sherry
3 teaspoons cornstarch
2½ teaspoons packed light brown sugar
1 tablespoon oyster sauce
2 teaspoons rice vinegar
2 teaspoons coarsely ground pepper
3 tablespoons plus 1 teaspoon vegetable oil
1 red bell pepper (¼-inch-wide strips)
1 green bell pepper (¼-inch-wide strips)
6 scallions, white parts sliced thin on bias, green parts cut into 2-inch pieces
3 garlic cloves, minced
1 tablespoon grated fresh ginger
- Combine 1 tablespoon water and baking soda in medium bowl. Add beef and toss to coat. Let sit at room temperature for 5 minutes.
- Whisk 1 tablespoon soy sauce, 1 tablespoon sherry, 1½ teaspoons cornstarch, and ½ teaspoon sugar together in small bowl. Add soy sauce mixture to beef, stir to coat, and let sit at room temperature for 15 to 30 minutes.
- Whisk remaining ¼ cup water, remaining 2 tablespoons soy sauce, remaining 2 tablespoons sherry, remaining 1½ teaspoons cornstarch, remaining 2 teaspoons sugar, oyster sauce, vinegar, and pepper together in second bowl.
- Heat 2 teaspoons vegetable oil in skillet over high heat. Add half of beef in single layer. Cook without stirring for 1 minute. Continue to cook, stirring occasionally, until spotty brown on both sides, about 1 minute longer. Transfer to bowl. Repeat with remaining beef and 2 teaspoons vegetable oil.
- Return skillet to high heat, add 2 teaspoons vegetable oil, and heat. Add bell peppers and scallion greens and cook, stirring occasionally, until vegetables are spotty brown and crisp-tender, about 4 minutes. Transfer vegetables to bowl with beef.
- Return now-empty skillet to medium-high heat and add remaining 4 teaspoons vegetable oil, scallion whites, garlic, and ginger. Cook, stirring frequently, until lightly browned, about 2 minutes. Return beef and vegetables to skillet and stir to combine.
- Whisk sauce to recombine. Add to skillet and cook, stirring constantly, until sauce has thickened, about 30 seconds. Serve immediately.