Rinse dried shiitake mushrooms under running water; Soak them in water for 15 minutes; Remove them; Fill a bowl with 400ml water; Put the dried shiitake mushrooms into the bowl of the water; Leave it for 3 hours; Remove and drain them; Discard the stems with a pair of kitchen scissors; Cut the remaining into pieces with a vegetable knife.
Hold freshwater drum firmly by the head and scrape the scales from the tail towards the gills with a fish scaler; Rinse the fish under running water; Insert the knife into the anus near the tail; Draw the knife toward the head, splitting the fish to the base of the gills; Spread the abdominal cavity with fingers; Reach in and pull out the entrails; Rinse the cavity under running water; Cut off the head with the knife; Rinse the fish under running water again; Pat-dry the fish with kitchen paper.
Place the freshwater drum on a chopping board again; With the point of a filleting knife, cut the fish to the bone behind the gills, across the tail, and around the edge of the flesh; Slice along the backbone from the head to the tail, down to the bone; Holding the knife almost flat, slide it under the flesh, beginning at the backbone; Keeping the knife flat, use a gentle sawing motion to ease away the first fillet from the bones; Repeat on the other side of the backbone for the second fillet (Repeat the step for the other side of the fish)
Rinse the fish fillets; Pat-dry them with kitchen paper; Remove any bones with a pair of tweezers, and discard any skin; Cut them into pieces; Put them in a mixing bowl; Marinate with seasoning (1) for 30 minutes.
Rinse and drain spring onion; Cut off any roots; Julienne it.
Rinse, drain, peel and julienne ginger.
Rinse eggs under running water; Dry them with kitchen paper; Break them over a mixing bowl; Whisk the egg solution with a flat whisk.
Add seasoning (3) into a mixing bowl; Mix.
Fill a stockpot with 2100ml water; Bring to the boil over a high heat; Add the dried shiitake mushrooms, the ginger, the ham and most of the spring onion (including 400ml dried shiitake mushroom soaking water); Bring to the boil over a high heat again; Turn to a medium heat; Cook over a medium heat for 20 minutes; Add the fish and seasoning (2); Bring to the boil over a high heat again; Turn to a low heat; Cook over a low heat for 10 minutes; Stir the seasoning (3) into the soup over a low heat till it thickens; Turn off the heat; Immediately but gradually stir the egg solution into the soup; Leave it for 1 minute; Arrange the soup into serving bowls; Garnish the soup with the remaining spring onion; Ready to serve.