In a large bowl, combine the soy sauce, sake, grated ginger, minced garlic, salt, and black pepper. Add the chicken thighs, ensuring they are fully coated in the marinade. Cover and refrigerate for at least 1 hour or overnight for best results.

Prepare the Coating

In another bowl, mix together the cornstarch and all-purpose flour to create the coating for the chicken.

Heat the Oil

In a deep pan or fryer, heat the vegetable oil over medium-high heat until it reaches 180°C (350°F).

Coat and Fry the Chicken

Remove the marinated chicken from the fridge. Take each piece of chicken and dredge it in the cornstarch and flour mixture, shaking off any excess. Carefully place the chicken pieces into the hot oil and fry in batches for about 4-5 minutes or until golden brown and cooked through. Ensure not to overcrowd the pan.

Drain and Serve

Once cooked, remove the chicken from the oil and place it on a plate lined with paper towels to drain excess oil. Serve hot with spicy mayo on the side.