Marinate the prawns with the turmeric and salt in a shallow dish in a cool place for 30 minutes to an hour.
Heat 60ml/2fl oz of the oil in a pan and add the bay leaves and onion paste. Fry gently for 6-8 minutes on medium heat, or until very light brown.
Meanwhile heat the remaining oil in a non-stick frying pan and fry the prawns briefly for a minute or two. Set aside.
Mix the ground cumin, turmeric and ginger-garlic paste in 75ml/2½fl oz of water and add to the onions, reduce the heat and cook for 2-3 minutes stirring regularly.
Add salt, green chillies and the prawns and stir for one minute. Mix in the coconut milk and simmer for 2-3 minutes, or just until the prawns are cooked, adding a little shellfish stock if necessary.
Season to taste with sugar. Sprinkle over the cardamom powder and coriander and a squeeze of lime. Serve with some boiled basmati rice.