Soak 12 dried shiitake mushrooms in hot water, 30 minutes. Remove the stems. Boil 4 quartered heads bok choy, 2 minutes. Stir-fry 1 minced garlic clove in peanut oil, then add the mushrooms and some thinly sliced jicama; stir-fry 1 minute. Add 2 tablespoons each oyster sauce and mirin (sweet rice wine) and 1 cup chicken broth; cover and cook, 5 minutes. Add 2 teaspoons cornstarch mixed with a splash of water, then the bok choy; stir-fry 2 minutes.