Doi Ilish (Hilsa with curd)

Marinate fish with little salt,turmeric and curd.Heat 2 tbsp oil and add the marinated fish.Add water,turmeric,red chilli powder and salt and pinch of sugar to taste.Grind the mustard posto with 1 green chilli and pinch of salt. When nearly done add the mustard posto paste,green chillies and sprinkle 1 tbsp mustard oil.Give it a boil and serve hot with rice.Mustard paste should always be added at the end when the fish is almost done to retain it's tingling flavour.