This is a traditional Bengali recipe which involves cooking lentils with the fried head of carps.
Carps are river fishes and huge heads of carps are available for sale separately in fish markets.It is very popular among the people living in Eastern part of India.
One can cook with any sea fish also.But I recommend adding grated coconut to the dish in that case.Coconut dilutes the strong smell of the sea fishes.
We find it excellent when served with hot steamed rice.
Bengali, Bong, East Indian
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2.1tbsp.Bengali all spice powder [cinnamoncardamom, black pepper and cloves mixed in equal proportion and grounded]
3.Tomato puree [1/2 cup] optional
4.Onions chopped[1/2 cup]
5.Gingergarlic and green chilies paste [2 to 3 tbsp. ]
6.Fish head 
7.Red chilly powder [1 tbsp. ]
8.cumin powder [1 tbsp. ]
9.coriander powder [1 tbsp. ]
10.turmeric powder [1 tbsp. ]
11.salt as per taste
12sugar [1/2 or 1 tbsp. ]
13.green chilies [2 to 3 slit]
14.Mustard oil [1/2 cup]
15.Ghee [1 tbsp. ]
16.Bay leaves [1 or 2]
1.Dry roast the lentils or moong dal till light golden brown by continuous stirring it over medium flame
2.Wash the lentils.
3.marinate the fish heads with salt and turmeric for 5 minutes.
4.Add mustard oil and heat it .
5.Fry the fish heads in oil till crispy.
6.Take out the fish heads from oil.
7.In the remaining oil add all spice powder and bay leaves
8.Add oinons and fry till golden
9.Add ginger garlic paste and saute
10.Add tomato puree and remaining spices ,turmeric,cumin powder,chilly etc
11.Add the lentils and add two cups of water.
12.cover and cook till the lentils are soft and get blended well.It should not be mushy.
13.Add salt and sugar at this stage.
14.Add the fish heads and with a ladle break the heads lightly.
15 Add slit green chillies and a tbsp of ghee and serve it hot with steamed rice.