Pour 3/8 litres of boiling water over Mu-Err mushrooms and soak for about 30 minutes. Drain the bamboo on a sieve and cut into bite-sized pieces. Clean, wash and cut leek and pepper into fine strips.
Wash the chicken filet, dab dry and cut into strips. Clean shiitake mushrooms, wash carefully and drain. Mix chicken stock, cornstarch, 2 tablespoons soy sauce, ketchup, vinegar, sugar, Asian sauce and 1/2 teaspoon sambal oelek.
Drain Mu-Err mushrooms, clean them and cut them into smaller pieces depending on their size. Heat some oil in a wok, fry meat and shiitake in it. Take out, heat remaining oil and steam vegetables and Mu-Err mushrooms for 4-5 minutes while stirring.
Put the meat and shiitake mushrooms back in the wok. Add sauce, bring to the boil and simmer everything for 1-2 minutes. Season to taste with soy sauce, Sambal Oelek and China spice mixture.