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 1/4 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.