• 2 fresh red chillies
• 400 g ripe medium tomatoes
• 5 cm piece fresh root ginger
• 4 large cloves garlic
• 1 medium-large onion
• 5 tablespoons groundnut oil, plus extra for frying
• 2 rounded teaspoons ground turmeric
• 1 kg firm-fleshed white fish fillet, skinned
• 1 rounded teaspoon soft brown sugar
• 2 tablespoons fish sauce
• 300 ml water
• juice of 1 lemon
• bunch of spring onions

Cut open the chillies under running water, discard the seeds and stems, then chop the flesh finely. Pierce each tomato with the tip of a sharp knife, then put them into a bowl, cover with boiling water and leave for a minute or two before draining. Peel the tomatoes and chop the flesh fairly small. Peel the ginger and garlic and chop finely together. Peel the onion and chop finely.

In a large bowl, mix 3 tablespoons of the groundnut oil with the turmeric. Slice the fish into large chunks, add to the bowl and rub all over with the oil and turmeric mixture. Heat a thin film of oil in a large frying pan over a high heat. When it is smoking, add the pieces of fish and fry for a minute only on each side, turning them gently. Remove from the heat and set aside.

Pour any remaining turmeric-infused oil from the bowl into a flameproof casserole. Add the remaining groundnut oil and place over a medium heat. Add the onion and stir over the heat until soft and browned, then add the ginger and garlic and stir around for a minute or two. Add the tomatoes and chillies and cook, stirring, for about 5 minutes until the tomatoes are mushy. Stir in the sugar, fish sauce, water and lemon juice. Take off the heat.

Add the fish carefully, so as not to break up the pieces, and pour in any remaining pan juices. Cover the casserole and set over the lowest possible heat - the juices should barely bubble. Cook for 10-15 minutes, depending on the thickness of the fish, until it is just cooked.

Meanwhile, slice the spring onions across into 5 cm pieces, using as much of the green part as you can. When the fish is ready, add the spring onions, cover again and cook for another 2 minutes. Serve at once.