For the marinade: whisk egg white lightly in a large bowl, then whisk in the soy and Mirin. Set aside half of marinade for the dry coat. Add the soda and cornflour to one half of it and whisk to combine. Add chicken to large bowl and stir to coat thoroughly.
For the dry coat: whisk together the flours, baking powder, and salt. Add the reserved marinade and whisk until mixture has looks like breadcrumbs. Press the chicken into this mixture and shake off the excess. Place on a rack over a tray and place in the fridge for an hour.
Turn the Actifry on for 2 minutes to heat up. Add a tablespoon of oil and heat for a further minute. Add the chicken and cook for five minutes, then go in with some tongs to help separate some of the chicken pieces that may have stuck together. Cook for a further 25 - 30 minutes, until crisp and at least 68C on the inside.
Five minutes before the chicken is ready, fry the garlic, ginger, and onions in a frying pan over a medium heat. Combine soy sauce, wine, vinegar, stock, sugar, sesame seed oil, and cornflour in a small bowl and stir with a fork until dissolved and no lumps remain. Stir the sauce into the onions etc until it boils and thickens. Add the chicken and fold with a rubber spatula until all pieces are thoroughly coated. Serve with rice and mixed vegetables.