Rui Shorshe(Rohu fish in mustard paste)

Sprinkle little salt and turmeric to the cleaned fish.Meanwhile soak mustard in hot water for 10 minutes.Then make a paste of it with 1 green chilli,curd and little salt.Heat oil and fry the fish golden brown.Sprinkle kalonji(nigella) and add tomato puree.Add salt,turmeric and red chilli powder.Toss and add the fish.Add 1 cup water and boil.Add the mustard paste and boil for sometime.Add 2 tsp mustard oil and garnish with chopped coriander and green chillies.Serve hot with rice.