1. Marinate 250 gms cleaned fish head with 4 gms salt and 1/2 tsp turmeric powder. set aside.
2. Heat a thick bottomed kadai or wok and dry roast 100 gms moog dal / yellow split gram while continuously stirring on medium heat. we want the dal to be evenly pinkish brown.
3. Transfer to a pot and wash with cold water to stop cooking further.
4. Wash the roasted dal, then drain the water. add 5 gms of salt and 300 gms water and set it to boil, partially covered with a lid until the dal is cooked but still holds shape. the dal should not break because it is going to cook again with the fish head.
5. Heat 25 gms mustard oil in a pan and fry the fish head on low heat until well browned on all sides. set aside the fried fish head on a plate.
6. In a bowl weigh out 1/2 tsp turmeric powder, 3 gms cumin seeds, 1/4 tsp kashmiri red chilli powder, and 12 gms ginger paste. make a slurry with a couple of tablespoons of water.
7. Heat mustard oil in korai, and temper with 2 dried red chillies, 2 bay leaves, 2 green cardamom, 2 cloves, 1 inch cinnamon and 1/2 tsp cumin seeds.
8. Add 15 gms diced onion and fry for 5 minutes or until golden .
9. Add 15 gms chopped tomatoes and cook until they soften.
10. Next add the spice slurry prepared and fry until the raw smell of spices goes away. also add 2 slit green chillies and fry.
11. Add the fried fish head. braise with the spices.
12. Add the boiled moog dal and 275 grams of hot water. add 3 gms salt and 20 gms sugar. cover and simmer on low heat for 2 minutes.
13. Take out 2 tablespoons of the liquid from the top of the dal. mix this thoroughly with a 1/4 tsp atta (whole wheat flour) in a bowl. add this back to the korai. this atta will help thicken the dal and prevent the water and the dal from completely separating when stored.
14. Simmer until the dal thickens lightly for about 2 minutes.
15. Turn off the heat. finish with one slit green chilli, 8 gms ghee and a pinch of bengali garam masala. give it one final stir, cover tightly with a lid and rest for 15 minutes before serving.
16. Serve in the beginning of the meal (after bitters or greens) with boiled rice. serve a bhaja like beguni or jhuri alu bhaja as a side.