I got the original teriyaki recipe from here. It takes only 10-15 min make, and the sauce is way better than the usual teriyaki sauce that is served in American Japanese restaurants.
potato starch （片栗粉）
Japanese eggplant or chicken thighs/breast
[sauce mix]: 2 tbp soy sauce + 1 tbp sugar + 1 tbp mirin + 1 tbp cooking rice wine
For the soy sauce, I use the usukuchi soy sauce （薄口醤油）to get a lighter color. For cooking rice wine, I use Shaoxing rice wine instead of normal cooking rice wine for a nuttier and richer taste. Depending on how much eggplant/chicken you have, you can make more of the sauce --- just double or triple the mixture.
(1) Coat the eggplant or chicken with potato starch
(2) In a frying pan, heat up 2-3 tbp of vegetable oil, then put the eggplant/chicken in on medium heat. Flip it once until both sides are slightly brown. If it looks like the pan is getting dry, you can add more oil to prevent it from blackening.
(3) Add 1/2 of sauce mix to the pan, and immediately cover to simmer for 1-2 min, making sure that the sauce mixture is well absorbed by the starch coating. Uncover, flip once and add the other half of the sauce; soak the sauce on the other side.
(4) Depending on your liking, you can either serve it immediately after the sauce is completely absorbed and the eggplant is still soft, juicy, and meaty; or you can wait until the absorbed sauce is slightly evaporated and the eggplant becomes a little crunchier. Your call.
Serve hot and eat!