A recipe originating in West Bengal from Madhur Jaffrey’s “Flavours of India.”
Run 1/2 tsp turmeric and 1/2 tsp salt over the fish steaks. Set aside for 10 minutes.
Heat the oil in a wide non stick frying pan over a medium high heat. When hot, add the fish and fry on each side for 2-3 minutes until golden. Remove with a slotted spoon and set aside.
Meanwhile put the tamarind paste, cayenne, sugar, remaining salt, remaining turmeric and 7 fl oz water into a bowl and mix well.
Take 2 tbsps of the oil used for frying the fish and heat a clean frying pan over a medium high heat. When hot put in the mustard seeds and as soon as they start to pop the tamarind mixture. Bring to the boil over a medium high heat.
Turn the heat to low and simmer for 10-12 minutes, stirring often, until the oil bubbles at the surface and the sauce is very thick.
Return the fish to the pan and simmer for 5-8 minutes, turning the fish once very gently during this time. The sauce should just coat the fish.