Shorshe Ilish (Hilsa Fish in Mustard Sauce)

Method

Soak the brown and yellow mustard seeds in cold water for 30 minutes — this softens them enough for grinding. Drain, then grind with green chillies and ginger using a pestle and mortar or spice grinder into a coarse, grainy paste. Do not over-grind; the texture should catch in the sauce.

Heat the mustard-oil in a heavy-bottomed pan over medium-high heat until it reaches smoking point, then reduce to medium. This burns off the oil's raw bitterness. Fry the hilsa steaks for 2 minutes per side until just golden, then lift out carefully and set aside. Hilsa is delicate — use a wide spatula.

In the same oil, fry the sliced onions until soft and translucent, about 5 minutes. Add the mustard paste and turmeric, stirring continuously for 2 minutes so the paste fries rather than steams. Add water and salt, scraping any caramelised bits from the base of the pan.

Return the fish to the pan. Simmer uncovered on the lowest heat for 15-20 minutes until the sauce reduces and coats the back of a spoon and the fish flakes when pressed. Taste for salt.

Serve hot with plain steamed rice, spooning the mustard sauce generously over each portion.