Thoroughly wash the pomfret fish and marinate it with 1 teaspoon each of turmeric powder, salt, and mustard oil. Let it sit at room temperature for 15 minutes, which you can use for other preparations.

Separately soak black mustard seeds (kalo shorshe) and poppy seeds (posto) in hot water for 10 minutes.

Drain the water and put the mustard seeds and poppy seeds into a blender with 2 green chilies, 2-3 garlic cloves, and ½ teaspoon of salt. Blend these ingredients into a paste. Alternatively, you can use a traditional grinding stone, called a shil-nora or shil batta, to do this by hand.

Some people dilute this mixture with water, remove the husks, and use only the flavorful liquid for the gravy. If you prefer a rustic, earthy gravy, do not strain the mixture; use it as it is. However, for a creamy, subtle gravy, use the diluted version. Both methods work well.

Make a paste of the tomato(s), which you can also chop. Both methods work well, but they offer different depth of flavor.

Next, slice the green chilies.

Now, heat three tablespoons of mustard oil in a pan or kadhai until it changes color and begins to smoke.

Carefully place the marinated fish into the pan, one by one, to fry. Avoid overcrowding the pan, as pomfret is a delicate fish.

Keep the heat high and fry each side for no more than one minute. Do not over-fry the fish.

Continue frying the rest of the fish in the same manner.

In the oil left in the pan, add kalojire (nigella seeds or kalonji) and the green chilies for tempering.

Cook for about a minute until they release a pleasant aroma. From this point, keep the flame at a medium setting.

Now, add the tomatoes and cook for two minutes over a low flame.

Add the mustard and poppy seed paste, mixed with one cup of water, to the pan. Then, stir in one teaspoon of turmeric powder, one teaspoon of red chili powder, and half a teaspoon of salt.

Simmer the mixture until it begins to boil, which should take about 2-3 minutes.

Adjust salt if needed.

Next, add the fried fish and cook for a maximum of 2 minutes.

Then, flip the fish and cook for one more minute.

For extra flavor, you can stir in some chopped cilantro (Dhonepata / Coriander leaves) at this stage.

If you prefer a thinner gravy, add an additional cup of water when you originally add water; otherwise, the one cup is sufficient for a semi-thick consistency.

Finally, drizzle one tablespoon of mustard oil over the top, gently mix, and turn off the heat.

Serve the hot pomfret fish curry with steaming rice.