1. In a large bowl, combine butter, onion, capsicum and celery; cook for 2-3 minutes on high.
2. Stir in flour, tomatoes, tomato paste, chicken stock, parsley, sugar, salt and chilli powder; mix well.
3. Cook, uncovered, for 5 minutes on high, stirring once.
4. Add prawns and cook for 10-12 minutes on medium, stirring twice.