Wash the dried shiitake mushrooms of any sediment and soak them in enough cold water to cover for at least 3-4 hours (or until soft) before cooking. Or, soak them overnight (up to 8 hours) in the refrigerator. Drain the rehydrated mushrooms. (Reserve the mushroom soaking water for future braises, stews, and noodle soups!) You can halve or slice the larger pieces if desired.If your dried shiitake are large and woody or didn't soak for long, you can trim the bottom centimeter of the stem as desired. We never remove the stems, and don't usually have a problem with toughness if properly soaked in cool water. The long, gentle stewing also helps!
Clean and quarter the bird. Keep the skin on but remove the extra fat (this can also be reserved for future stir-fries). Divide chicken in half and chop into manageable 2-3 inch sections, reserving the other half to freeze or cook another day. For the size of our 5.5 qt Dutch oven, half a chicken is more than sufficient. Wash and rinse the chopped meat until water runs clear.
Place the chicken, cooking wine, ginger and scallions into a large (about 6 qts) heavy-bottom pot and fill with cold water roughly 75% full. Cover and bring to a boil. When you hear it boiling, turn the heat down low and continue simmering for 10 minutes but do not uncover during this time.
After 10 minutes, uncover the pot and skim clean all the scum that rises to the surface. Skim some of the oil from the surface as well to keep the soup from feeling too greasy. When all the scum is gone and no longer rising to the surface, add the rehydrated shiitake mushrooms. If you need to add more water from this point on, use hot water, never cold water. Continue simmering, covered, on the lowest possible heat for 2-4 hours depending on the maturity of the bird and desired flavor. It is done when the soup tastes strong enough to your liking and the meat falls off the bone, although it is still old hen and won't be tender. (In the pressure cooker, the bones actually become soft enough to eat. Yes, eat!)
Keep warm and wait to salt-season until ready to serve. Dunjitang is excellent whether served Cantonese-style as the first course, Sichuan-style as the last course, on its own, or as the base for wonton and noodle soups!