Combine the rice wine or mirin, ginger, salt and black pepper in a bowl; mix well. Add the chicken and coat.
Put the flour and cornstarch into a bag, shake to mix, and add the chicken pieces one at a time; shake the bag to cover all the pieces. Dip the chicken into the buttermilk, let drain and then coat again with the dry mixture.
In a large skillet or dutch oven, add about 1/2" of oil and heat it until the oil temperature reaches 350 F and sizzling. Add the battered chicken carefully, skin side down. Do not crowd. It will not be completely covered with the oil.
Keep heat at medium to medium high just enough that the oil is always bubbling and cook for 10 minutes, making sure not to burn the coating.
Turn the chicken over, skin side up, cover the pan but allow the steam to vent and cook for another 10 minutes.
Check for doneness; fried dark meat can cook as high as 175-180 for fall off the bone meat, white meat needs to come out at 165 degrees.
Turn up the heat a bit and continue to fry for just a minute per side to make sure the skin is crispy. Remove from heat and drain on paper towels.
In a medium saucepan, combine all of the Korean fried chicken sauce ingredients. Heat the sauce over medium low heat and stir well. Once it starts bubbling, remove the pan from the heat.
Place the fried chicken into a large mixing bowl then pour the fried chicken sauce over the chicken to coat. Mix them lightly and thoroughly. Alternatively, serve the fried chicken and the sauce separately and use the sauce as a dipping sauce. Serve immediately; it's best when hot.
Garnish if desired with toasted sesame seeds and green onion.