In a strainer add 1½ tbsp of yellow and 1½ tbsp black mustard seeds, wash under running water, and grind with green chillies to a smooth paste by using your food processor. From this mustard paste use 4 tbsp for making Sorshe Ilish. You can use rest (if anything left) of the paste for making mustard-based fish or vegetable curries.

Or else, you can use ready to use mustard powder (Sunrise brand). If cooking with the mustard seeds powder, use 4 tbsp of it and follow the package instructions for dissolving.

If you’re cooking with ready to use mustard powder then make a green chilli paste separately of 6-7 green chillies along with some water in a food processor.

In a bowl add mustard paste, 2 tbsp mustard oil, 1 tsp turmeric powder, salt (as per taste), nigella seeds. Now whisk the curd until smooth and add into the mustard mixture. Add in the green chilli paste also if you're using store brought mustard powder. Mix well and keep it aside.

Now take a container that is well fitted into your pressure cooker (read note). Arrange the freshly washed fish pieces in the box, pour the paste over it, add some water as per your requirement of the gravy (I used ¼ cup ) and spread 2-3 tsp of mustard oil on top along with a few slitted green chillies which will add some extra flavour into it. Close the container tightly.

Place the container inside the pressure-cooker and pour some water inside of the cooker (the water level should be halfway up to the container). Close the lid. Start heating over medium heat. After two whistles turn off the heat. Wait until the steam inside gets dissipate.

Bring out the container carefully and open it. Your Doi Ilish Bhapa is ready to eat, serve hot with steamed rice. Enjoy!