Add cooking oil to a deep frying pan and switch on the heat to medium.
Marinate the fish with 1/4 tbsp of salt and rub to evenly distribute it. Sprinkle the rest of the salt and repeat. Set aside.
Submerge dry wooden cooking chopsticks and observe if tiny air bubbles are formed in the oil. This indicates the oil is ready for deep-frying.
Strip all the curry leaves from the stem and add them to the cooking oil. Fry for 20-30 seconds, and remove them all with a strainer.
Coat each fish fillet with crispy flour completely, shaking off the excess. Immediately add it to the hot oil, repeating with the rest of the fillets.
Fry them for 3 minutes without turning or moving the fish. When the bottom has completely cooked, it will detach from the pan itself.
After 3 minutes, turn the fillets to the other side and fry for another 3 minutes. After that, turn the fish every minute or so, until fully golden brown.
Remove the fillets with a strainer, and rest it in a bowl to drip off the excess oil. Set it aside. Switch off the heat.
With a clean pan, heat up the Kam Heong sauce over medium heat.
Add all the Kam Heong sauce to the pan, and spread it evenly.
Add 100ml of water and stir until slightly thinned. If the consistency is too dry, add another 50ml of water (optional). Continue stirring for about 1 minute, until fully hot and runny.
Add all the fish fillets and stir until well coated with the sauce, for about 1 minute.
Add the curry leaves and give it a light toss. Switch off the heat.
Transfer to a serving plate and serve with some rice.