Clean and wash prawns and remove tail(optional). Slice onions lengthwise. Roast coconut and 3-4 onions and curry leaves together on medium heat till browned. Add chilly powder and coriander powder and mix well and keep aside to cool. Start cooking prawns with 1-2 cups of water, tamarind paste and turmeric powder. Bring to boil and then reduce heat medium and continue cooking. Meanwhile, heat 1tbsn oil in a pan and saute the remaining onion till the raw smell is gone. Gound the coconut mixture to a fine paste adding enough water. 5. When prawns is 3/4 th done, add onion and ground coconut and add more water if gravy is ery thick. Add salt and cook on medium heat till prawns is done and gravy reaches the requred consistency. 5. Serve with rice. Make this 3-4 hours earlier for better taste. This can be refrigrated for 2-3 days.