1. Heat butter in a heavy saucepan, add onion and garlic, stir gently until soft.

2. Mix spices and seasoning to a paste with vinegar and tomato ketchup.

3. Add mixture to the pan and fry for 3 minutes, stirring continuously.

4. Stir in Grace coconut milk and simmer for 10 minutes. Add prawns and allow to cook in sauce for 5 minutes.

5. Transfer to a heated serving dish and serve immediately.