Grate the ginger and squeeze it over a bowl to extract it's juices. Add the sake or wine and soya.
Cut the chicken thighs into four chunks and rub well with the marinade, then set aside in the marinade for 30 minutes.
Heat the oil slowly for 165-170oC/330-340oF. Pat the chicken dry on paper towel. When the oil is hot, dust the chicken generously with cornflour and lower the pieces into the oil. To maintain the oil temperature, do not add too many chicken pieces at once. Deep fry the chicken pieces for 4-5 mins, until crisp, golden and cooked through.
Halve on chicken piece to make sure it is cooked inside. Drain the rest of the chicken, then serve hot or cold.