Bihari Fish Curry (sarso Wali)

River fish the way Bihar cooks it no shortcuts, no compromises. Rohu or katla, lightly fried first to seal the flesh, then slow cooked in a sharp mustard oil gravy with turmeric, green chillies and freshly ground spices. The colour is golden. The flavour is bold. The mustard cuts through everything and stays with you. This is a dish that smells like someone's kitchen in Bihar, the kind where the mustard oil hits the pan and the whole house knows what's for lunch.