Place the dried shiitake in a bowl. Cover with hot water. Place a plate over the mushrooms to weigh them down. Leave to rehydrate for about six hours.
Remove the mushrooms from the soaking liquid. Cut off and discard the stems. Cut the caps into quarters.
Strain the soaking liquid.
Boil about six cups of water in a pot. Drop in the chicken thighs and legs. Boil vigorously for about five minutes.
Drain and rinse the chicken.
Wash the pot (discard the water) and pour in the strained mushroom liquid. Add enough water to measure a total of six cups.
Add the chicken, ginger (with its juice) and about a tablespoon of salt to the liquid in the pot and bring to a simmer.
Lower the heat, cover the pot and cook the chicken for 10 to 15 minutes depending on how large they are.
Taste the broth. Add more salt if needed. Add the mushrooms to the chicken and simmer for another 10 minutes.
Taste the broth once more and sprinkle in more salt, if necessary.
Add the bok choy to the chicken and mushrooms. Simmer for another 5 to 10 minutes or until the bok choy stalks are tender.
Give the broth a final taste test and adjust the seasoning, if needed, before serving the chicken, shiitake and bok choy soup.