Preheat the oven to 180C (350F).
Put the tomatoes, sugar, lemongrass, curry paste, coriander seeds and cumin in a blender or mini chopper and process to a paste.
Heat the rapeseed and sesame oil in a large (lidded) casserole and then stir fry the shallots, garlic and chillies for 2-3 minutes.
Add the turmeric, butter and rice and stir until the rice is coated. Add the paste and stir to mix everything together.
Add the prawns and kaffir lime leaves and stir fry them for a minute. Stir in the fish sauce, coconut milk and stock and bring to the boil.
Cover and transfer to the oven. Cook for 20 minutes then take the lid off, stir, and cook for a further 5-10 minutes until liquid is reduced and rice is cooked.
Serve with a sprinkling of crushed peanuts and garnish with a few coriander leaves.