When the monsoon sets in, a plate of steaming rice paired with a sharp, tangy mustard fish curry can turn an ordinary meal into something special. This dish has been a staple in Bihari households for generations, yet plenty of people who did not grow up cooking it are unsure where to start. If that describes you, here is the full method laid out step by step. What sets this curry apart is its bold, tangy gravy, built around a finely ground paste of yellow mustard and garlic, and it tastes best when eaten alongside a bowl of plain rice.
What You Need
For the fish, you need 500 grams of rohu or katla fish, half a teaspoon of turmeric, half a teaspoon of red chilli powder, a teaspoon of garlic paste, salt to taste and mustard oil for frying. For the spice paste, gather two teaspoons of yellow mustard, a teaspoon of black mustard, 10 to 12 garlic cloves, a teaspoon of cumin seeds, half a teaspoon of black peppercorns and two green chillies. For the gravy, you need two medium tomatoes, half a teaspoon of fenugreek seeds for the tempering, a teaspoon of coriander powder, half a teaspoon of turmeric powder, a teaspoon of Kashmiri red chilli powder, salt to taste, and finely chopped coriander leaves for garnish.
Marinate and Fry the Fish
Start by washing the fish pieces thoroughly. Mix in the turmeric, red chilli powder, garlic paste and a little salt, then set the fish aside for about 15 minutes so the spices soak in properly. Meanwhile, heat mustard oil in a pan until it just begins to smoke, which is what removes its raw, pungent edge. Fry the marinated fish on medium-high heat, turning it so both sides turn golden and crisp, then remove the pieces and keep them aside.
Make a Fine Mustard-Garlic Paste
Add the yellow mustard, black mustard, garlic cloves, cumin seeds, peppercorns and green chillies to a blender jar along with a little water, and grind everything into a completely smooth paste. The finer this paste is ground, the better the final gravy tastes, since any coarse grains left behind can leave the curry tasting raw and bitter, so it is worth taking the extra minute here.
Roast the Spice Base
In the oil left over from frying the fish, add the fenugreek seeds. Once they start to crackle, stir in the mustard-garlic paste and roast it on low heat for three to four minutes. Next, add the turmeric, coriander powder, Kashmiri red chilli powder and a splash of water, and keep roasting the masala until the oil starts to separate from it. Cooking the mustard paste slowly and thoroughly at this stage is essential, since it is what strips away the bitterness of raw mustard and gives the gravy a balanced flavour.
Build the Tomato Gravy
Once the spices are well roasted, add the chopped tomatoes and salt to taste. Cover the pan and let it cook until the tomatoes break down completely and blend into the masala. When the mixture starts releasing oil at the edges, pour in around two cups of hot water, adjusting the quantity to your preferred gravy consistency, and let it come to a good boil so the spices combine evenly.
Add the Fish and Serve
Once the gravy is boiling well, slide in the fried fish pieces. Cover the pan and let it simmer on low heat for five to seven minutes so the fish soaks up the full flavour of the gravy. Turn off the heat, sprinkle freshly chopped coriander leaves on top, and serve this Bihari-style mustard fish curry hot with steamed rice.
