Wood ears are dried fungus and are available in any Chinese supermarket. Before using, they should be soaked in a little warm water for about 20 minutes, then drained and patted dry.
Heat a wok, add some oil and stir-fry the sliced mushrooms and wood ear for 2-3 minutes, then add all the remaining topping ingredients and stir-fry for a couple of minutes until they have all softened.
Mix the ingredients for the soup base in a bowl, then add to the wok and bring to the boil.