In a small bowl, combine the ingredients for the sauce. Mix well and set aside.
Place the cubed chicken in a medium bowl and season with salt and white pepper. Add the cornstarch, mix well, then set aside.
Heat a wok or large pan over high heat. Once hot, add the peanut oil.
Add the garlic and red chiles, stirring for a few seconds, then add the chicken and stir-fry for a couple of minutes.
When the chicken starts to turn opaque, add the sherry and cook for 2-3 more minutes.
Add the sauce and bring the mixture to a boil.
Reduce the heat to medium and continue to simmer until the chicken is cooked through and the sauce has thickened, another minute or two.
Turn off the heat, discard the red chiles, and stir in the scallions to serve.