In a bowl, combine the soy sauce, mirin, sake, and sugar and mix togeter
In a small saucepan over medium heat. Pour in the sauce and whisk to dissolve the sugar
Bring the mixture to a gentle simmer, and cook for 5 to 6 minutes, stirring occasionally.
If using cornstarch to thicken, mix 1 teaspoon of cornstarch with 1 tablespoon of cold water in a small bowl until completely smooth.
Add the cornstrach mixture to the simmering sauce and stir constantly for 60 seconds until the sauce visibly thickens and turns glossy.
Remove the teriyaki sauce from heat and set aside to cook.
If not using cornstarch, continue reducing the sauce until it reaches your desired consistency, about 10 to 12 minutes.
Score the thighs using a sharp knife by making 2 to 3 shallow diagonal cuts across the thickest part of each thigh
After scoring the chicken, marinate it in the teriyaki sauce we prepared earlier for 30-minutes or better yet, overnight
Place a skillet over medium-high heat
Add 2 tablespoons of a neutral oil.
Place the chicken thighs skin-side down into the hot pan
Let the chicken sear untouched for 5 - 6 minutes
Once timer is up, flip and cook the second side for 4 to 5 minutes
Reduce the heat to medium-low
Pour the prepared teriyaki sauce into the pan around and over the chicken.
Once the sauce starts bubbling, use a spoon to baste the chicken with sauce from the pan and pour it over the top of each chicken piece
Continue basting for 2 to 3 minutes until the sauce reduces to a thick, glossy glaze that coats the chicken in a visible, shiny layer and barely moves when the pan is tilted.
Your chicken is now done. Remove the pan from heat.
Transfer the chicken to a warm plate and let it rest for 5 minutes before cutting
Slice each chicken thigh against the grain and enjoy over some rice
Spoon the remaining sauce on top.
Garnish with sesame seeds and enjoy!
