Pick the leaves off the celery stalk and reserve for later use. Cut the celery stalk into 2-inch lengths. In a mortar, combine the celery, chile, spring onion (white part only), and garlic then slightly pound into a coarse paste. Pour the fish stock into a large pot and bring to the boil.
Add the cod cutlets, sugar, and fish sauce, and then bring back to the boil skimming out any impurities. Add the celery stalk-chile mixture.
Reduce the heat to a low simmer and cook for 10 minutes. Now add the tomatoes, celery leaves, and spring onions (green parts) and cook for another 5 minutes. Take the pot off the heat and transfer to a large bowl, then add the bean sprouts, and lime juice and stir.
Serve the soup with the jasmine rice and side dipping sauce of sliced chile and fish sauce.
Recipe courtesy of Luke Nguyen