Tap on clams to see if they automatically close and discard non-responsive one; Discard any clams with broken/cracked/ chipped shells.
Fill a large mixing bowl with water; Stir 1/3 cup of salt and ¼ cup of cornmeal into the water; Submerge the clams by the mixture to expel the dark matter and sand from the clams’ stomachs and whiten the meat; Leave it for 4 hours; Remove the clams; Rinse the clams under running water; Scrub the outside of the clams thoroughly with a stiff brush to get rid of any barnacles, coral, sand or other debris; Place the clams in a bowl of cool fresh water with a damp towel on the top; Chill them in a freezer for 20 minutes.
Rinse and drain Chinese celery; Pull off leaves; Trim coarse stems off; Slice off the tough bask; Cut the remaining stems into sections.
Rinse, drain, peel and slice ginger.
Fill a deep plate with water; Stir 2 tsp salt into water; Carefully arrange firm tofu into the salty water; Leave it for 30 minutes; Discard the salty water; Cut the tofu into cubes.
Remove the clams from the freezer and let them sit a few minutes before starting shucking job; Shuck each clam over a bowl with a clam knife to save all the wonderful juice known as clam liquor; Sieve the clam liquor for later use.
Add 1 tsp oil to a wok; Heat over a high heat; Add whole peppercorns and the ginger; Stir-fry over a high heat till fragrant; Turn off the heat; Transfer it into a stockpot.
Fill the stockpot from the step 7 with 1.5L fish broth and 1L water; Bring to the boil over a high heat; Add all the ingredients (including the clam liquor); Bring to the boil over a high heat again; Turn to a medium heat; Cover the pot with its lid; Cook over a medium heat for 30 minutes; Stir seasonings into the soup; Turn off the heat; Arrange the soup in serving bowls; Ready to serve.