Rinse dried Chinese yam under running water; Soak it in water for 3 hours; Remove and drain it.
Rinse and drain American ginseng.
Rinse and drain dried burdock slices.
Rinse, drain, peel and slice ginger.
Hold sea brass 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.
Fill a pot with 2.5L water; Add the American ginseng, the dried burdock slices and the dried Chinese yam; Bring to the boil over a high heat; Turn to a low heat; Cover the pot with its lid; Cook over a low heat for 2 hours.
Add 2 tbsp oil to a non-stick pan; Add the ginger and stir-fry it over a high heat till fragrant; Turn to a low heat; Arrange the fish into the pan; Turn to a high heat; Pan-fry the fish over a high heat till both sides are slightly brown; Turn off the heat; Transfer the fish together with the ginger into the soup from the step 6; Turn to a medium heat; Cook over a medium heat for 10 minutes; Turn to a low heat; Cover the pot with its lid again; Cook over a low heat for 30 minutes; Stir seasonings into the soup; Turn off the heat; Arrange the soup in serving bowls; Ready to serve.