Peel and grate ginger and crush (or mince) the garlic. In a large bowl, whisk all the ingredients for the marinade.
Cut each skin-on chicken thigh into 5 to 6 pieces, about 1 ½ inch pieces.
Lightly season the chicken with kosher salt and freshly ground black pepper.
Add the chicken to the marinade. Coat and rub the chicken with marinade using your hands/tongs. Set aside for 30 to 60 minutes.
In a medium bowl, combine potato starch and rice flour and whisk well.
In a pot, heat the oil to 340ºF (170ºC). I use a smaller 1 ½ QT pot, so that oil is deep enough and I don't have to use much oil. Use a thermometer or wooden chopsticks to see if the oil is ready (See How to Deep Fry Foods).
When the oil is hot, drain the chicken well from the marinade and coat each piece with the flour mixture.
Deep fry for 90 seconds, or until the chicken is light golden color. Work with a few pieces at a time, so the oil temperature won’t drop quickly. I worked with 3 to 4 pieces at a time.
Transfer the chicken to a wire rack to drain excess oil. Let the chicken cook with the remaining heat while you work on the rest of the chicken.
Once the chicken is all deep-fried for the first round, use a fine-mesh sieve to pick up crumbs to keep the oil clean. If you don't do this step, the crumbs get darker, and then the oil gets darker.
Increase the heat and bring the oil to 350ºF (180ºC). Deep fry the chicken for the second time for 45 seconds or until crispy and golden brown. Transfer the chicken to a wire rack to drain excess oil.
Serve the chicken immediately with lemon wedges, parsley, lettuce, and shichimi togarashi. If you like, squeeze the lemon before you eat and sprinkle shichimi togarashi for spice.