Heat the rapeseed oil in a cooking pot and add the mustard seeds. When they finishing popping add the curry leaves, stir for 30 seconds then add the chopped onions.
When the onions become translucent in colour add the chilli garlic paste and cook for a further 2 minutes.
Add the spices and tomato puree and cook for 30 seconds then add the tomatoes, jaggery and shrimp paste. Cook for 10 minutes until thickened and then add the prawns and cook for 3-4 minutes until done.