Tare Sauce

Place 12 chicken wing tips, 250ml (1 cup) boiling water, 2 dried shiitake mushrooms and a pinch of salt in a small saucepan and simmer for 1 hour. Drain, retaining only the liquid. Peel a 3cm (1¼in.) piece of fresh ginger and slice thinly. Return the liquid to the pan, add 150ml (⅔ cup) soy sauce, 150ml (⅔ cup) mirin, 2 cloves of garlic and the ginger, and heat gently for 20 minutes until just before boiling point. Combine a little potato flour with a little water, reduce the heat and gradually add the flour mixture until you have a thick, smooth sauce.