1Cut the Chicken thighs, boneless, skin-on into bite-sized pieces, approximately 3-4 cm. In a bowl, combine the chicken with Soy sauce (for marinade), Mirin, Garlic, minced (for marinade), Ginger, grated (for marinade), and White pepper powder. Mix well and marinate for at least 20 minutes at room temperature.
2While the chicken marinates, prepare the mala sauce. In a small dry pan, toast the Sichuan peppercorns over medium heat until fragrant, about 1-2 minutes. Grind them finely using a mortar and pestle or a spice grinder. Set aside.