Wash and clean fish.

Pat the fish dry, coat lightly with salt and ½ tbsp turmeric, and set aside.

Soak the tamarind in warm water and extract the pulp; reserve.

In a blender, grind 2 tbsp white mustard seeds with one green chilli and a pinch of salt into a smooth paste.

Heat 6 tbsp mustard oil in a deep pan over medium heat. Shallow-fry the fish until just cooked and lightly golden; transfer to a plate.

In the same oil temper, 1 tbsp kalajeera. Add the white mustard paste, 1 tbsp turmeric, 1 tbsp chilli powder, two whole green chillies, and salt. Stir, then pour in 1 cup water and bring to a boil to form the “Ganga” gravy. When slightly thickened, immerse one side of each fish piece and cook for 2–3 minutes; keep aside.

In a separate pan, heat the remaining 3 tbsp mustard oil. Temper 1 tbsp dark mustard seeds until they crackle, then add the tamarind pulp, ½ tbsp chilli powder, two green chillies, sugar, and salt. Cook until this “Jamuna” gravy thickens.

Place each fish piece back into this pan so the opposite side is coated in the Jamuna sauce. Cook for 2–3 minutes more, then transfer to a serving platter.

Drizzle 1 tbsp fresh mustard oil over the top and serve immediately with hot steamed rice.