First, prepare the chicken for frying. Lightly beat the eggs in a bowl, then cut the chicken thighs into bite size pieces, mixing with the eggs. Using a large resealable container, combine the flour and the cornstarch. Take out the chicken pieces one by one and add them to the flour mixture. Pop on the lid and give the box a good shake, coating the chicken.
Heat up some vegetable oil in a wok. When hot, add the chicken pieces one by one and fry until golden brown- about 3-5 minutes. Allow the chicken to drain on a wire rack or some kitchen roll.
Preparing the nanban sauce is simple. Simply combine all the ingredients, bring to the boil and then reduce to a simmer. Continue to simmer for a minute, then turn off the heat. Remove the kombu piece when finished.
Using chopsticks, dip the chicken pieces into the nanban sauce and swirl around thoroughly until all the chicken is well coated. Assemble the chicken on a serving dish.
For the tartar sauce mix onions, lemon juice and mustard, then stir in the eggs and cucumber. Top the chicken generously with tartar sauce and enjoy.