The cooking of this dish goes quickly, so makes sure you have all your ingredients ready before turning on the stove. If you wish, ½ cup shiitake mushrooms, stemmed and minced, can be added to the dish.
2 tablespoons soy sauce
1 tablespoon dry sherry
1 teaspoon sugar
½ teaspoon cornstarch
¼ teaspoon ground white pepper
¼ teaspoon red pepper flakes
¼ teaspoon dry mustard
2 tablespoons water
2 tablespoons vegetable oil
1 pound green or yellow wax beans, ends trimmed, cut into 2-inch pieces
3 medium garlic cloves, minced
1 tablespoons minced fresh ginger
3 scallions sliced thin
1 teaspoon toasted sesame oil
In a small bowl, stir together soy sauce, sherry, sugar, cornstarch, white pepper, chili flakes, mustard, and water until sugar dissolves; set aside.
Heat oil in a 12-inch nonstick skillet over high heat until just smoking. Add beans and cook, stirring frequently, until crisp-tender and skins are shriveled and blackened in spots, 5 to 8 minutes (reduce heat to medium-high if beans darken too quickly). Transfer beans to large plate.
Reduce heat to medium, add a teaspoon of oil and add minced shiitakes to now-empty skillet. Cook 2-3 minutes, until mushrooms are soft. Add garlic and ginger, cook, stirring constantly, until fragrant, 15-20 seconds. Stir sauce to recombine and return beans to pan with sauce. Toss and cook until sauce is thickened, 5-10 seconds. Remove pan from heat and stir in scallions and sesame oil. Serve immediately.