Soak the shiitake in hot water for no less than 30 minutes.
Rinse the mushrooms, cut off and discard their stalks and slice the caps thinly.
Put the cold water in a medium saucepan and add the ginger, star anise, mirin, shoyu and roughly chopped spring onion. Slowly bring to the boil, add the carrot and shiitake and simmer for a further 15 minutes.
Add the Chinese cabbage then cook for a further 5 minutes.
Remove the ginger and star anise and serve the soup with a garnish of chopped coriander and spring onion.