Preheat the grill to medium heat. Sprinkle the coconut onto a baking tray and toast under the grill until just golden-brown. Set aside.
Put the basmati rice in a lidded saucepan then cover with 400ml/¾ pint cold water. Add half of the butter, then cover the pan, place it over a high heat and bring just to the boil. Reduce the heat to its lowest setting and cook the rice for 12-15 minutes, or until the rice has absorbed all the water and is just tender.
Meanwhile, heat the vegetable oil in a frying pan over a medium heat. Add the onion and stir-fry for 2-3 minutes, or until just softened. Add the curry paste and stir-fry for a further minute.
Add the chicken to the pan and stir well to coat it in the sauce.
Add the tomatoes and coconut milk, stir well and bring the mixture to the boil, then reduce the heat until the mixture is simmering and simmer for 10 minutes, or until the chicken is cooked through and the sauce has thickened slightly.
Stir in the chopped coriander, mint and lime juice, then stir in the remaining butter and season, to taste, with salt and freshly ground black pepper.
To serve, fluff the cooked rice using a fork, then divide it equally among four serving plates. Spoon a ladleful of chicken curry on top of each portion of rice. Garnish with a sprinkling of desiccated coconut.