To make the Marinade:

• Prepare a thick paste of Black Mustard either in grinder or with the help of “Silnora” or “Shil Batta” by adding 1 green chili and 1 Tsp. of salt and keep it aside.
• Make Paste of Poppy Seeds or Posto separately.
• Rub fish pieces with ½ teaspoon salt and ½ teaspoon turmeric powder and Chilli Powder and leave those for 10 minutes.

To prepare the box full of marinated fish for steaming:

• Now in a bowl add Mustard Paste, Poppy Seed Paste, Freshly Grated Coconut, Sour Curd, Red Chilli Powder, Turmeric Powder and 3 Tbsp. of Mustard Oil and Mix properly.
• Add salt to the mixture. Do check the salt as we have already added salt while rubbing the fish and in the Mustard Paste. Add 1 Cup of Water to the mixture.
• Add Green Chilli.
• Bhapa Ilish can be prepared in a flame using a double boiler or can be prepared in Microwave.
• Take a Stainless Steel Tiffin Box or a Microwave oven safe Container with a tight lid and rub some Oil in the container.
• Now spread half of the previously prepared Paste the container and put 2-3 slit Green Chilies and then place Fish pieces and finally pour rest of the paste over the fishes.
• Pour 1 Tbsp. of Mustard Oil on the top and also rest of the slit Green Chilies.
• Cover the lid of the tiffin box.

Steaming the Ilish: Any of the process mentioned below can be followed:

Using Vessel or Handi:

• Take a deep Vessel/ Handi with and place the Box and then pour 5 Cup of water in the box and place the stainless Steel box and then cover the Vessel with the lid and place the vessel on high flame for around 5 minutes or till water started boiling and then cook on low flame for around 20 minutes.

Using Pressure Cooker:

• Pour 5 Cup s of water in a Pressure Cooker and place the Stainless Steel Box and then Pressure cook in a pressure cooker on medium flame for 2-3 whistles. Wait till steam comes out of the cooker.

Using Microwave oven:

• Take a Microwave safe deep vessel and put the Container containing Fish and then put 5 Cups of water and Cook in High Temperature for 5 minutes and then in 40% temperature for around 25 minutes.
• Carefully take out the tiffin box and open the lid.
• Bhapa Ilish is ready to serve with steamed rice.