Marinate the Chicken: Combine the garlic, ginger, soy sauce, sake, and sesame oil in a bowl to create your marinade. Add the chicken pieces, ensuring they are fully covered by the marinade. Let the chicken marinate for at least 1 hour, but if possible, leave it in the fridge overnight for maximum flavor.
Prepare for Frying: Remove the chicken pieces from the marinade, shaking off any excess liquid. Roll each piece of chicken in potato starch, ensuring that it is fully coated. Shake off any excess starch.
Place coated chicken in fridge for 30-60 minutes, allowing potato starch to hydrate. Excess potato startch pieces will not fry properly.
Heat the Oil: Pour the oil into a deep pot or deep fryer, ensuring there's enough oil to completely submerge the chicken pieces. Heat the oil to 170-180°C (340-350°F).
Fry the Chicken: Fry the chicken pieces in batches to avoid overcrowding the pot. Cook each batch for about 6-8 minutes, or until the chicken is golden brown and fully cooked through. Use a slotted spoon or Spider to remove the chicken pieces from the oil, and let them drain on a rack or a paper towel-lined plate.
Serve: Serve the karaage hot, with a side of Japanese mayo for dipping and lemon wedges for squeezing over the chicken.