Fish and Chip Shop Curry Sauce

1 onion
1 apple, peeled
1 tablespoon curry powder
2 tablespoons oil
2 tablespoons flour
20 ounces water
1 tablespoon tomato puree or 1 tablespoon tomato paste
pepper
lemon juice

1. Chop the onion and apple and fry with the curry powder in the oil until tender.
2. Stir in the flour, cook for 2 minutes and then remove from the heat and add
the water, tomato puree, pepper and lemon juice to taste.
3. Simmer for 15 minutes.
4. Store refrigerated.