Melt butter, add curry powder, chopped celery, onion and chopped capsicum.
Saute gently for 2-3 minutes.
Peel and chop tomato, add to pan, cook for a further 2 minutes. Stir in flour, salt and pepper, cook 1 minute. Gradually add water and milk
add crumbled stock cubes.
Continue stirring until sauce boils and thickens.
Reduce heat, add sugar and lemon juice simmer 20-25 minutes, stirring occasionally.
Add prawns, allow to just heat through.
Serve with hot rice.