Flatten chicken breasts with a rolling pin and season with salt, then coat in flour.
Beat the egg in a shallow dish and place breadcrumbs in another. Dip chicken in egg, then coat in breadcrumbs.
Melt butter in a pan and sweat diced onions until cooked through.
Add curry powder and chicken stock to onions, bring to boil, then stir in soy sauce and mirin. Simmer for about 10 minutes.
Heat vegetable oil in a frying pan. Fry chicken for about 5-7 minutes on each side until golden and crispy.
Mix cornflour with water and stir into the sauce to thicken. Adjust consistency with more chicken stock or water if needed.
Serve cooked rice, slice chicken, place on top, and pour over katsu curry sauce.
