Trim any tendons and excess skin from the chicken. Place the chicken in a plastic bag with the cooking sake and let it marinate for a while. Thinly slice the garlic and cut the onion into thin slices about 1/4 inch (5mm) wide.

[Make the sauces] In a bowl, combine all [A] ingredients and mix well. In a separate bowl, combine all [B] ingredients and mix well.

Pat the chicken dry with paper towels. Sprinkle with black pepper, then lightly coat with potato starch (or cornstarch), shaking off any excess.

Heat the vegetable oil in a skillet. Add the garlic, onion, and a pinch of salt (not listed in ingredients). Sauté over medium heat until caramelized, then remove from the pan and set aside.

Increase the heat to medium-high. Place the chicken skin-side down in the pan and cook until browned. Flip the chicken, add 1 tablespoon sake, cover, and steam over low heat for about 5 minutes.

Remove the lid, add the [A] sauce, and simmer over medium heat until the sauce thickens and coats the chicken. Add the sautéed onion and garlic back in and mix to combine.

Cut the chicken into bite-sized pieces and plate. Drizzle with the mayonnaise sauce and sprinkle with chopped scallions.