How to Make It
In a medium bowl, toss the chicken with 1 tablespoon of the soy sauce, 1 tablespoon of the sherry, and the 1 tablespoon cornstarch.
In a small bowl, combine the sugar, vinegar, sesame oil, water, and the remaining 4 tablespoons of soy sauce, 1 tablespoon of sherry, and 2 teaspoons cornstarch.
In a wok or large frying pan, heat 1 tablespoon of the oil over moderately high heat. Add the peanuts and stir-fry until light brown, about 30 seconds. Remove from the pan. Heat the remaining 1 tablespoon oil. Add the white part of the scallions and the red-pepper flakes to the pan and cook, stirring, for 30 seconds. Add the chicken with its marinade and cook, stirring, until almost done, 1 to 2 minutes. Add the soy-sauce mixture and the scallion tops and simmer until the chicken is just done, about 1 minute longer. Stir in the peanuts.
Variation: Cashew Chicken: Substitute the same amount of cashews for the peanuts.