Fish Vevichaathu

Tiring of Fish and Chips and Goa fish curry on Fridays, I tried this recipe from Sanjeev Kapoor's Khana Khazana, thinking that it would be similar to Elina's Red Fish Curry.
It was nice enough, but not the Malayalee Red Fish curry that I was hoping for. What turned out well however, was the Basa fish that I used. I thought it would fall to pieces in the curry, but it firmed up nicely and stayed flaky and tender.  I also changed a few ingredients based on what I had in my kitchen

 500-600 gms of Basa or Pomfret if you can get it
2 tablespoons of Mirin, or any other vinegar

 Dry the fish thoroughly and cut into 10 centimeter slices.  If you are using Basa fillets, cut each into three.
Sprinkle the Mirin and salt over the fish and ensure its evenly spread over, and leave aside
 1" ginger
3-4 pods of garlic
6 cocums or a small walnut sized ball of tamarind

 Grind garlic and ginger into a paste - or you can just use 2 teaspoons of a readymade paste
Soak cocums or tamarind in 1/2 cup warm water for 15 minutes or longer if possible, especially if you are using cocum. If tamarind, strain out the seeds and fibres and discard.
 2 onions, chopped finely
 2 green chilli, -deseeded and chopped
Curry leaves - about ten
1 tablepoon mustard seeds
2 tablespoons oil, or a good glug. I used extra light Olive oil as its quite tasteless.

Place a wide shallow pan that will hold the fish in a couple of layers only, and pour the oil in. After a couple of minutes throw in the mustard seeds. Stand back smartly, as they will start popping out, add the curry leaves when they stop popping, then the onion, and stir till the onion turns golden.  Add the ginger-garlic paste and fry till the raw smell vanishes. Turn the heat down.
 1 teaspoon haldi or turmeric powder
1 tablespoon Kashmiri chilli powder
1 tablespoon coriander powder
1 Tomato, chopped

 Add to the onion-ginger-garlic paste and stir. Add the tomato immediately after, this will prevent the powdered spices from burning. Add the soaked cocum or tamarind (and water), stir well and simmer for 5 minutes.
Add the fish carefully in a layer mixing the masala gently over it.
 1.5 cups warm water
 Pour into the pan, bring to the boil rapidly. Turn down the heat,  cover the pan tightly and simmer for 10-15 minutes.

Serve immediately with hot rice and steamed french beans.