Peel the prawns without removing the head and the tail, better. Devein with the help of a toothpick. Mix them with 1 teaspoon turmeric powder and a pinch of salt and set aside.
Cut the onion into squares and blend them in a blender.
Heat the oil in a frying pan. Fry the prawns on each side for a few seconds. It has to be for a very short time, otherwise, the prawns will have a chewy texture.
Remove the prawns and set them aside. In this same oil (which has all the flavour of the prawns) add all the whole spices: bay leaf, cardamoms, and cinnamon stick.
Add the onion paste and fry until the water from the onion evaporates. Add ginger paste, turmeric powder, red chilli powder and a little bit of salt. Fry for a few minutes until oil separates.
Add the coconut milk and a little bit of water. Stir everything well and bring to a boil. Then add prawns and salt. Let cook on medium heat for 5-6 minutes.
Turn off the heat. Add fresh green chillies and garam masala. Cover and leave to rest for another 5 minutes before serving.
Serve it with hot Basmati rice.