In a medium bowl or container, combine chicken with grated ginger, garlic, soy sauce, cooking sake, white pepper, and salt. Mix well, cover, and marinate in the fridge for at least 30 minutes – or up to 24 hours for deeper flavor.
In a separate bowl, mix the potato starch and all-purpose flour.
In a wok or deep saucepan, heat oil to about 180 °C (355°F). Do not fill the wok more than half way to avoid overflow while frying.
Lightly coat the marinated chicken with potato starch. Fry in batches, ensuring enough space for each piece to float without crowding. Fry for 3-5 minutes, or until golden and fully cooked (cooking time may vary depending on the size of the pieces).
Drain excess oil using a rack or kitchen paper. Serve hot with lemon wedges and Japanese mayonnaise, and a sprinkle of parsley if desired.
