Begin by patting the chicken thigh fillets dry with paper towels to ensure the marinade clings well. Place the chicken in a bowl or ziplock bag, then add the soy sauce, cooking sake, mirin, and freshly grated ginger. Massage the marinade into the chicken, ensuring every piece is coated. Let it marinate for 30 minutes to 1 hour.

In a deep pot, pour enough vegetable oil to create a depth of about 3-4 cm, ensuring there’s plenty for proper frying. Heat the oil to 160°C (320°F).

Drain the excess marinade from the chicken and place it on a clean plate lined with paper towels. Sprinkle corn flour evenly over the chicken, tossing it gently to ensure each piece is well coated.

Carefully add the coated chicken to the hot oil in small batches, frying for about 2.5 to 3 minutes, or until lightly golden. Remove and place on a plate lined with paper towels.

Remove any floating crumbs from the oil and increase the temperature to 190-200°C (374-392°F) for the second fry.

Return the rested chicken to the hot oil in batches and fry for an additional 30 seconds to 1 minute until deeply golden-brown.

Arrange the crispy Japanese Karaage Chicken on a serving platter atop a bed of shredded lettuce or cabbage. Optionally garnish with sprigs of parsley.