Add the soy sauce and mirin, stir constantly for 3 minutes, then add the ginger. Cook for a further 2-3 minutes until the sauce has reduced to a lovely thick glaze.
Add1 cup of water (250mls). Mix well then place a lid on the pan and simmer for approx. 45 minutes. Stir every 10 minutes, check to make sure that it is on a low simmer, and add a little more water if the pan is getting dry.