Clean and cut the fish into pieces. Set aside.
Soak the kudampuli in warm water for about 10-15 minutes. Tear it into smaller pieces if needed and set aside.
In a small bowl combine turmeric, Kashmiri red chilli powder, pepper powder, salt and a bit of water to form a paste. Set aside.
In a clay pot (manchatti) or deep pan, heat coconut oil.
Add mustard seeds, and when they splutter, add fenugreek seeds.
Sauté ginger, garlic, and onions until they turn golden brown.
Lower the heat and add the masala paste. Sauté the spices for a minute, adding a little water to prevent burning and to cook the spices thoroughly.
Cook them until the raw smell of the spices is gone.
Add soaked kudampuli (including the water) to the pan and bring it to a boil.
Pour in additional water as needed to make the gravy. Boil for 3 -4 minutes.
Gently place the fish pieces in the curry, ensuring they are covered with the sauce.
Cover the pot and cook on low heat until the fish is cooked through and the oil rises to the top, which usually takes about 10-12 minutes.
Add fresh curry leaves and a drizzle of raw coconut oil for extra flavour.
Let the curry rest for a few hours or overnight for the best flavour, as the spices will intensify.
This curry is best enjoyed the day after it's made, as the flavours deepen and meld together. The Kottayam-style fish curry is a delightful combination of spiciness and tanginess, typical of Kerala cuisine.
Serve hot with steamed rice or Kerala parotta.