Clean 500 grams of prawns and marinate them with 1 teaspoon of turmeric powder and salt for 30 minutes.
Dry roast 1 cup of grated coconut, 5 dry red chillies, 1 tablespoon of coriander seeds, 1 teaspoon of cumin seeds, 1/2 teaspoon of fennel seeds, 1/2 teaspoon of peppercorns, 4 cloves, 1 inch of cinnamon stick, and 4 green cardamoms until they turn golden brown. Let it cool.
Grind the roasted ingredients with 1 chopped onion, 4 cloves of garlic, and 1 inch of ginger to make a smooth paste.
Heat 2 tablespoons of oil in a pan, add 1 chopped onion and sauté until it turns golden brown.
Add the ground paste to the pan and cook for 5-7 minutes.
Add the marinated prawns to the pan and mix well. Cook for another 5 minutes.
Add 1 cup of water and salt as per taste. Cover the pan and let it simmer for 10-15 minutes until the prawns are cooked and the gravy thickens.
Garnish with fresh coriander leaves and serve hot.