method
1. Chop onion, add to fat and cook until tender.
2. Blend in flour and add tomato juice, sugar, paprika, salt, cayenne and lemon juice.
3. Cook, stirring constantly, until thickened.
4. Add tuna and pour into casserole. Cover with potatoes.
5. Bake in moderate oven (350°F.) about 20 minutes or until potatoes are browned.
