Cut 250 g boneless chicken thigh into bitesize pieces and place them in a container.
Add 2 tsp Japanese soy sauce (koikuchi shoyu), 1 tsp sake, ½ tsp grated ginger root and ½ tsp grated garlic. Mix thoroughly and make sure all of the chicken is coated, then cover and marinate in the fridge for 10 minutes.
Kurozu an Sauce
Take a jug or bowl and add 3 ½ tbsp light brown sugar, 2 tbsp apple vinegar, 1 ½ tbsp Japanese soy sauce (koikuchi shoyu), 2 tsp Japanese black vinegar (kurozu), 2 tsp mirin, 1 tbsp sake, 1 tbsp water and 1 tsp cornstarch. Mix until the sugar and cornstarch are fully dissolved and set aside for later.
Prepping
Take a large frying pan and add about 2cm cooking oil (approx 1 inch). Heat the oil to 180 °C (356 °F). While you wait for the oil to heat up, cut the vegetables.
Roughly cut 100 g eggplant with the skin on, and soak in cold water for 5 minutes. If you're using 50 g lotus root (renkon), peel it and cut it into thick slices, then place them in the bowl with the eggplant.
Peel 75 g carrot and cut it into rough pieces. Cut the 100 g green bell pepper and 75 g onion into roughly 2cm (approx 1 inch) squares.
Frying
Once the oil has finished heating, add the carrot and fry for 3 minutes on each side.
Remove the carrot and place on a wire rack to allow the excess oil to drip off.
Remove the eggplant and lotus root from the water and dry each piece thoroughly with kitchen paper. Place each piece into the oil along with the green pepper and fry for 1 minute.
After one minute, remove and drain on the wire rack.
Add the onion to the oil and fry for 1 min. Once finished, transfer to the wire rack and reduce the heat to 170 °C (338 °F).
Sprinkle 2 tbsp potato starch (katakuriko) onto a plate and roll each piece of marinated chicken in the starch before placing it into the oil.
Fry the chicken for 3 minutes on each side.
After 6 minutes in total, increase the heat to 190 °C (374 °F) and fry for 1 more minute on each side.
Transfer the chicken to a wire rack to allow the excess oil to drip off.
Finally, heat a large frying pan or wok on medium, add a small drizzle of oil and then add the fried vegetables and chicken. Take the jug of sauce from earlier and give it a mix before pouring it into the pan.
Stir fry until the sauce has thickened and coats the chicken and vegetables.
Serve up and enjoy!
Notes
If you don't want to shallow fry the vegetables, you can stir-fry the vegetables. Just note that this will change the overall texture and look of the dish, and will also take longer to cook.
If you can't get black vinegar, mix 1 tsp of rice vinegar with 1 tsp balsamic vinegar.