Begin by gently patting the chicken pieces dry using paper towels to remove excess moisture. Place the chicken into a ziplock bag or bowl along with the soy sauce, sake, mirin, and freshly grated ginger. Make sure the marinade thoroughly coats the chicken—massage it well if using a bag. Let the chicken sit in the marinade for 30 minutes to 1 hour to soak in the flavors.
As the chicken marinates, prepare a deep pot or heavy-based frying pan and pour in enough vegetable oil to reach a depth of 3–4 cm (about 1¼–1½ inches). Heat the oil to a stable 160°C / 320°F (Note 3).
When ready to cook, remove the chicken from the marinade and place the pieces on paper towels to drain any excess liquid. Transfer the chicken to a clean bowl and evenly sprinkle the corn flour over the surface. Toss or turn each piece so they are uniformly coated.
Fry the chicken in small batches to avoid overcrowding. Carefully lower each piece into the hot oil, one at a time. Cook for 2½ to 3 minutes, adjusting placement if necessary to prevent the chicken from sticking to the bottom of the pot or pan.
Once lightly cooked, remove the chicken from the oil and let it rest on paper towels for at least 3 to 4 minutes. This step allows the juices to settle and helps prevent the final coating from becoming too greasy. Repeat the process for the remaining batches.
After all the chicken has been pre-fried, skim off any flour debris floating in the oil. Increase the oil temperature to 190–200°C / 374–392°F (Note 3) for the second fry. Return the chicken pieces in batches to the hot oil and fry for an additional 30 seconds to 1 minute, or until the exterior becomes crisp and golden.
Serve the hot, crispy chicken immediately with shredded cabbage or lettuce, and a few sprigs of fresh parsley for garnish if desired.