Bengali fish curry (Macher jhol)

1. Cut the fish into 5-6 cm pieces and rub with 1 teaspoon turmeric and 1 teaspoon salt. Cut the potatoes and aubergine into long batons and sprinkle with a little turmeric and salt too.

2. Heat the mustard oil in a frying pan until smoking (this mellows its flavour), fry the fish for 2 minutes on each side until golden and lift out. Fry the potatoes and aubergine in the same oil for 4-5 minutes and lift out.

3. Add the nigella seeds to the remaining oil and, when they sizzle, the green chillies, slit lengthways.

4. Add the grated ginger, cumin seeds, the remaining turmeric and the diced tomato and cook with a little water for 4-5 minutes until pulpy.

5. Pour in the water, add the potatoes and cook for 10 minutes; then add the aubergine and fish and simmer for another 5-6 minutes. Jhol is a light, soupy curry: the sauce should stay thin.

6. Sprinkle with fresh coriander and serve with boiled rice.

Tip: "Macher jhol" means fish broth in Bengali; it's an everyday dish in Kolkata and Bangladesh, eaten from a deep plate with rice. Mustard oil gives it its typical slightly pungent flavour; if you have none, another neutral oil will do.