Cover shiitake in a bowl with 1 cup hot water. Let stand for 20 minutes.
Add the soaking water to a saucepan with 6 cups water, 1 spring onion, ginger, star anise, mirin and tamari. Bring to the boil slowly and add the carrots and sliced shiitake (stems removed).
Cook for 10-15 minutes.
Add bok choy and cook a further 2 minutes. Remove ginger and star anise. Place into serving bowls and add 1 tsp chopped coriander and 1 tsp chopped shallots. Serve.