Taste Pour one cup boiling water over shitake mushrooms and allow them to sit, covered for 30 minutes. When they are ready add the cornstarch to quarter cup of cool water and set aside. Slice the mushrooms into bite sized pieces, removing the stems, and pour the soaking liquid into a skillet. Add garlic and ginger. Simmer for a few minutes and then add the mushrooms, the bamboo shoots, the broth and the soy sauce. Simmer for at least 5 minutes. Steam the boy choy separately (2-3 minutes, checking and tossing often). whole baby bok choy may take a little longer. Add the bok choy to the mixture. Stir in the cornstarch till it's as thick as you like it. Serve over rice.