Pat the chicken dry with a paper towel to remove any excess moisture.
Add the teriyaki sauce ingredients, except the cornstarch, to a measuring cup or a jar. Mix thoroughly until the sugar is combined with the liquid.
½ cup Soy sauce, ½ cup Water, 4 cloves Garlic, ¼ cup Brown sugar, 1 tablespoon Shaoxing cooking wine
Place the chicken thighs in a large mixing bowl. Season the chicken with salt and pepper, and toss to coat. Pour ¼ of the teriyaki sauce onto the chicken thighs, and marinate for at least 10 minutes or up to 24 hours.
1 lb Chicken thighs, ½ teaspoon Kosher salt, ½ teaspoon Black pepper
Pour the remaining teriyaki sauce into a small saucepan, and bring it to a simmer over medium-low heat. Let the sauce simmer for approximately five minutes.
Mix the cornstarch and water into a slurry. Add the slurry to the sauce and stir constantly until thickened. Once the sauce is thick, take it off the heat.
1 ½ tablespoon Cornstarch, 1 ½ tablespoon Water
Heat a cast iron skillet over medium heat, with a tablespoon of oil. Place the chicken skin side down and let it sear until the skin is golden brown and the fat has started to render.
Brush the chicken with teriyaki sauce once you flip it over to cook the other side.
Cook the chicken thighs for 10-15 minutes, until the internal temperature reaches 165°F on a meat thermometer.