Bengali Mustard Fish (Machher Jhol / Shorshe Maach)

Ingredients

• 700 g firm white fish (such as rohu or similar freshwater fish), cut into steaks or fillets
• For the marinade
• 1 tsp ground turmeric
• 1 tsp salt
• For the mustard paste
• 2 tbsp black mustard seeds
• 2 tbsp yellow mustard seeds, equal parts to black; increase proportion of yellow for a milder result
• 2 green chillies, roughly chopped
• 60 ml water, added gradually during grinding
• 3 tbsp mustard oil, heated to smoking point before use
• 1 tsp ground turmeric, added to the sauce
• 200 ml water, to dilute mustard paste into cooking liquid
• 2 green chillies, slit lengthways, for finishing

Method

1. 1
   Rub the fish pieces with turmeric and salt, working both into every cut surface so the salt draws moisture from the centre of the flesh outward, firming the texture before cooking. Set aside to marinate for at least 20 minutes — the flesh will take on an even ochre stain and feel noticeably more taut when the time is up.
2. 2
   Grind the black and yellow mustard seeds with the chopped green chilli and water to a smooth, cohesive paste, adding the water gradually so the seeds break down fully rather than skating around a wet grinder. The paste is ready when no whole seeds remain and the texture is uniformly dense; taste it — the heat should be sharp and direct, the bitterness present but not dominant.
3. 3
   Heat the mustard oil in a wide, heavy pan over a high flame until a thin haze rises and the raw, acrid smell gives way to a nuttier, more settled aroma, because raw mustard oil carries a harsh edge that will dominate the finished dish if it is not driven off at this stage. Once the oil has calmed, reduce to a medium-high heat before proceeding.
4. 4
   Fry the marinated fish pieces in the smoked mustard oil, turning once, until lightly coloured on both sides so the exterior sets and will hold together in the sauce without flaking apart. Remove and set aside — the fish should be only partially cooked at this point, as it will finish gently in the simmering liquid.
5. 5
   This is where the dish lives or dies: add the mustard paste to the pan along with the turmeric and dilute immediately with the water, stirring to integrate paste and liquid into a unified, pungent, slightly opaque sauce, because mustard paste dropped into an undiluted, over-hot pan will seize and turn irrecoverably bitter rather than blooming into something complex and rounded. Work quickly and keep the heat moderate as you stir.
6. 6
   Return the fish to the pan and add the slit green chillies, then simmer gently, uncovered, until the fish is cooked through and the sauce has reduced to a consistency that clings without pooling. The fish is done when it yields cleanly to light pressure at its thickest point; serve directly from the pan while the sauce is still fragrant.