Ingredients :

• Rice vinegar — This is what defines the nanban sauce. Much milder than white vinegar — a rounded acidity, almost sweet, nothing aggressive. You can find it in supermarkets in the Asian aisle. A light apple cider vinegar can work in a pinch, but the result will be more rustic.
• Kewpie Mayonnaise — Not interchangeable with classic mayo. Creamier, richer in egg yolk, with a hint of built-in acidity that makes all the difference in the tartar sauce. Find it at Asian grocery stores or order online. Without it: mix normal mayo with a splash of rice vinegar — it’s a decent approximation.
• Rice syrup (instead of mirin) — Original mirin is a sweet Japanese condiment that gives shine and roundness to nanban sauce. We replace it with rice syrup — same effect, same amount. Otherwise, a tablespoon of honey diluted in a little warm water works very well.
• Chicken breast — Get thick breasts if you can. Thin fillets are less forgiving of frying and dry out quickly. The butterflying step is not optional — chicken of uneven thickness is a guarantee of one side being overcooked. If you prefer thighs, they stay juicier and are more tolerant of approximations.