Cut the chicken into bite-sized pieces (about 4cm) and place in a shallow dish.
Prepare the marinade and mix the grated ginger, grated garlic, soy sauce, sake, sesame oil and mirin in another bowl.
Coat the chicken with the sauce and cover your bowl to leave it overnight ideally or 30 minutes minimum in the fridge.
Heat the frying oil to 170°C or over medium heat.
Prepare a large bowl of potato starch and coat your chicken pieces in the starch. Feel free to be generous, they should be all white.
Once your oil is hot, dip the chicken pieces in for 3 to 5 minutes. They should be golden brown and crispy. We recommend cooking them in several batches.
Take them out even if they are white, wait for your oil to heat up, and dip your precooked chicken pieces back in. Repeat as many times as you like. Don't forget to skim off the excess cornstarch in your oil.