Clean and devein the prawns and add it to a bowl. Add in the turmeric powder, red chilli powder, salt and vinegar. Mix well and let the prawns marinate for 20 minutes.
Just before starting to cook, wash and soak the basmati rice in water. Aged basmati rice works well.
Heat coconut oil in a pressure cooker. Add in the marinated prawns. Do not add any water. Let the prawns cook in its own juices. Remove the prawns after 3-4 minutes and set aside on a bowl.
In the same oil used for frying prawns, add in the onions. Add in the salt and saute for 2-3 minutes till the onions are soft. Add in the crushed ginger-garlic-green chillies. Saute for 3-4 minutes till the onions are nicely brown.
Add in the tomatoes, mint leaves, coriander leaves and the curd.
Add in the garam masala powder. Cover the pan with a lid and let it simmer for about 10 minutes on a medium flame till the tomatoes are cooked and mushy.
After 10 minutes, you would notice that the oil is seperated and the masalas are well cooked.
Add back the prawns and butter. You can use ghee if you do not have butter.
Add in the hot water. The rice-water ratio I have used is 1 rice:1.5 water.
Drain the soaked rice and add it to the cooker. Mix well.
Cover the cooker and cook for exactly two whistles on medium flame. (About 7-8 minutes). Remove the cooker from heat and wait for the pressure from the cooker to settle.