First, we need to soak the mustard seeds separately in water for 10 minutes
Strain the mustard seeds and grind them one by one. Use one green chili and a little bit of mustard oil while grinding. I also use milk in place of water to grind and it gives a richer consistency.
The paste has to be of thick consistency. Once done, take a bowl and 2 tbsp of water and strain the black mustard paste. Discard the husk.
Grind the yellow mustard seeds with grated coconut.
In a mixing bowl, take both the pastes. Add turmeric powder, red chili powder, salt and 1 tbsp of mustard oil. Add the fish steaks in this marinade.
Take a tiffin box where you can place all the fish pieces side by side. Place the fish pieces with the marinade in this tiffin box.
Drizzle mustard oil and add few slit green chilies.
Close the lid and place the tiffin box inside a steamer for 15 to 20 minutes.
You can add water in a kadai and place the tiffin box in the kadai. Cover with a lid and let it cook in the steam.
You can also use a baking dish and bake in the oven for 15 minutes using the bain marie method.
It is also possible to cook this in a microwave and it takes only 5 minutes inside the microwave.
However, I find steaming or baking as the best options.
Serve bhapa ilish with steamed rice.