1. First marinate the prawn with salt, and turmeric, keep it aside.
2. Take a pan put it on the flame and add butter, then add marinated prawns, cook this prawn (75% done) and transfer it in a plate.
3. In the same butter, add onion paste, ginger garlic paste and cook this till raw flavor is gone.
4. Add chilly flakes, tomato paste, cook for few minutes. then add mustard paste, salt, green chills, pinch of sugar, coconut milk and then add prawns, cook this for few minutes.
5. Add garam masala powder, switch off the flame, put the lid on for few minutes. serve this hot with rice, and chapattis.