Clean and wash the fish slices and rub turmeric all over them. Cover and keep aside. Marinate for 15 minutes.
Grind to a Paste
Dry roast grated coconut in a frying pan over medium heat. Roast for 2-4 minutes or until the edges start to brown.
Push the roasted coconut to one side of the pan. Add coconut oil on the other side and allow to heat for 10-15 seconds. Add onion and sauté for 2-3 minutes. Stir and mix well.
Add dry red chillies and roast for another minute while stirring occasionally. Remove the mix from the pan and set aside to cool.
In the same pan, dry roast mustard seeds, coriander seeds, garlic cloves and black peppercorn for 2-3 minutes or until fragrant. Add tamarind to the pan, saute for 30 secs and remove from heat and set aside to cool.
Add both the roast mixes to a food processor or blender along with chopped tomatoes and water. Blend to a smooth thick paste.
For the Curry
Heat coconut oil in a large pan or kadhai over medium heat. Once the oil is hot, add the ground paste and mix. Add salt, red chilli powder and stir to combine. Bring to a boil, lower the heat and simmer for 10 minutes.
Slide the fish into the pan and mix gently so as not to break the fish. Simmer over medium heat for 10-12 minutes.
Remove from flame. Prepare tempering, add it to the curry, mix and serve hot along with some white rice.
For the Tempering
Heat coconut oil in a frying pan over medium heat. Once hot, add garlic and fry for 1-2 minutes or until the edges start to brown.
Add mustard seeds and curry leaves. Allow the mustard seeds to splutter. Remove from flame and add it to the curry. Mix and serve hot.
Use freshly grated coconut as far as possible. If using frozen, look for freshly grated frozen coconut. This is different from dessicated coconut which won't work here
Don't reduce the amount of garlic - that's where the flavour is
Grind the masala to a really smooth paste. Start with a little water and then add more if required
The consistency of the gravy should be thicker than milk - more like coconut milk
You know the gravy is ready when you see bits of oil floating on top
Oil: My choice of oil for this recipe is coconut oil, but a good replacement is ghee
Fish: Choose any firm white fish. Seer, mackerel, pomfret, red snapper, cod, sea bass will all work well here
Other proteins: Prawns, squid and even chicken work well with this gravy so throw in whatever you like. The cooking times for these will differ based on which protein you are using