Here, I used the tougher green tops of a leek, so I sautéed them in a frying pan with a little oil and salt (not listed). I used the same pan for the following steps with the chicken.
Warm the frying pan over medium-high heat, and add a little oil. Place the chicken thigh skin side down. It'll brown evenly if you press down the chicken as it's cooking.
Sauté until the skin turns golden brown and crispy, while wiping excess oil from the pan.
When your chicken resembles the photo here, flip it over. Pour in the combined teriyaki sauce, and cover with lid to simmer.
When the sauce has reduced to resemble the photo shown here, remove the lid. Coat the chicken with the sauce. Then wait to let the sauce simmer a little bit more, just until it is on the verge of scorching.
The glossiness of the sauce will remain even after the dish cools down. Slicing the chicken vertically will be easier while it is still hot. However, you'll also be able to slice it on the diagonal once it has cooled.
Place the chicken on a bed of sautéed leeks. You could also enjoy this dish with a little sansho pepper sprinkled on top.
Story Behind this Recipe
It's tough to make the perfect teriyaki chicken. Sometimes the meat might not be cooked through properly, the sauce might not be glossy enough, or the seasoning could be a little too subtle. I tried my hand at this dish a number of times to clear all these obstacles before settling on this recipe.
Make sure you wipe off any excess oil as you sauté the chicken. Sauté the chicken until the skin turns golden brown. Take your time simmering the teriyaki sauce to ensure that it is properly reduced before coating with the chicken.