Bring the first four ingredients to a boil in a large pot. Reduce heat and simmer for at least 10 minutes.

Meanwhile, slice the mushrooms and white part of the green onions, and chop the white stems of the bok choy.

Remove the spices from the broth with a slotted spoon.

Add the mushrooms, the whites of the onions, and bok choy stems to the broth. Simmer for a few minutes, until mushrooms are cooked through.

Stir in the soy sauce and remove from heat.

Measure the miso paste into a small bowl, and ladle some broth into it. Stir until miso paste is dissolved into broth, and pour into the pot.

Thinly slice the green onion tops and bok choy leaves.

Divide soup into 4 bowls, and top with leaves and tops of onions.

Garnish with sesame seeds if desired.