Rinse dried wood ear mushrooms under running water; Soak them in water for 3 hours; Remove and drain them.
Rinse, drain and slice ginger.
Rinse and drain water chestnuts; Cut off the top and the bottom of water chestnuts with a paring knife; Cut around the sides of each water chestnuts with the knife till all the skin is removed; Rinse them under running water.
Rinse lean pork under running water; Pat-dry it with kitchen paper; Cut it into pieces.
Fill a deep pan with water; Add 1 slice of the ginger; Bring to the boil over a high heat; Scald the lean pork all over in a colander with the boiling ginger water for 1 minute; Immediately remove it; Rinse it under running water till cool; Drain it; Turn off the heat.
Rinse apples; Drain them; Twist off any stems; Insert the sharp tip of a swivel peeler and run around the cores of the pears; Scrape out the cores inside; Cut the apples into chunks.
Fill a stockpot with 2880ml water; Add the remaining ginger slices and the dried wood ear mushrooms; Bring to the boil over a high heat; Add all the remaining ingredients and bring to the boil over a high heat again; Turn to a low heat; Cover the pot with its lid; Cook over a low heat for 2 hours; Scoop scum off with a perforated skimmer; Stir seasonings into the soup; Turn off the heat; Arrange the soup in serving bowls; Ready to serve.