1. Peel prawns, leaving heads and tails on. Slice one onion thinly and make a seasoning paste by grinding remaining onion with all other ingredients except ghee or oil.
2. Fry sliced onion in ghee or oil until soft, then add seasoning paste and fry for 4 minutes. Add water and simmer until sauce is thick and smooth. Put in prawns and cook for about 5 minutes or until tender. Do not overcook. Check seasonings and serve at once.
3. Thinly sliced fish fillets may also be cooked in this sauce.