Combine the soy sauce, sake, mirin and caster sugar into a small saucepan and place over a low heat. Keep stirring until the sugar dissolves and put to one side.
Heat the oil in a large non-stick frying pan over high heat.
Dip the chicken into the cornflour and shake off the excess. I skewer the chicken here but you don't have to.
Add to the pan carefully.
Cook for about 5 minutes until golden brown on both sides and just cooked through.
Reduce to medium heat and pour about half the teriyaki sauce over the chicken and bring to a simmer. Stir until the sauce thickens and the chicken becomes well coated.
Repeat with the remaining teriyaki sauce until it thickens.
Sprinkle the sesame seeds and coriander over the chicken and serve