1 pound boneless, skinless chicken breasts, cut into 1/2-inch chunks
3 tablespoons soy sauce
2 teaspoons cornstarch
Salt and ground black or Sichuan pepper
1 1/2 tablespoons Chinkiang (black) vinegar or balsamic vinegar
2 teaspoons sugar
1/4 cup neutral oil, such as grapeseed
1/2 cup small dried red chiles (15 grams; see Tip)
Mix the chicken, 1 tablespoon soy sauce, 1 teaspoon cornstarch, and a big pinch of salt and pepper in a bowl until evenly coated. Let sit while you prepare the sauce.
Stir the vinegar, sugar, remaining 2 tablespoons soy sauce and 1 teaspoon cornstarch in a small bowl.
Combine the oil and chiles in a wok or large nonstick skillet, and set over medium heat. When the chiles start to sizzle and brown, about 15 seconds, push them to one side of the pan. Add the chicken to the other side all at once and spread in a single, even layer. Cook, without moving the pieces, until the bottoms are dark golden brown, 3 to 5 minutes. If the chiles start to blacken, put them on top of the chicken so that they don’t burn.
Using a large spatula, flip the chicken in portions. Cook just until the meat almost loses all of its pinkness, 1 to 2 minutes more. Stir the sauce and pour it into the pan. Stir until the sauce thickens and slicks the chicken evenly. Immediately transfer to a plate and serve hot.
The small dried red chiles typically used in kung pao dishes are available in Chinese markets. Any small dried red chiles work, though they do range in heat. For a similar spice level, use chiles de árbol.