Take 4 pieces of hilsa fish. Marinate the fish with less than ½ tbsp of turmeric powder and less than ½ tbsp of salt. Smear the fish nicely and set it aside for 10 mins.
Create a paste using 1 ½ tbsp of black mustard seeds, 1 tbsp of yellow mustard seeds, 4 green chilis, and less than ½ tbsp of salt. Grind it using a grinding stone, then strain the paste with a strainer.
In a bowl, combine 1 tbsp of turmeric, ½ tbsp of coriander powder, ½ tbsp of cumin powder, and 1 tbsp of Kashmiri red chili powder. Add a little bit of water to prepare a mixture.
Take a wok and add 2 tbsp of mustard oil. Then, add the fishes and lightly fry them. After frying one side, flip them over and fry the other side. Avoid frying the hilsa fish too hard. Once fried, remove them from the oil.(Expert tip: Be very careful when adding the fish into the oil.) Now, add the previously prepared spice mixture to the remaining oil. Stir it nicely until the raw smell of the turmeric powder dissipates. After stirring, add the mustard paste to it and stir for 2 mins.
Add less than ½ tbsp of salt. When the stirring is done, it will release oil. Add 1 cup of water and 5 slitted green chilis into the gravy. Cover it and let it simmer.(Expert tip: Add salt according to your taste and adjust the water for your preferred gravy consistency.) When the gravy is simmering, add the lightly fried fishes. Cover it for 5 mins and let it cook. Turn off the gas when it’s done.
Drizzle 1 tbsp of mustard oil to enhance the taste, cover, and let it rest.
Ilish Macher Tel Jhal is ready and transfer it to a bowl.
Serve it with steamed rice.