COOL tempting meals can be made with all the weather is warm it's a good plan to cook fish just as soon as you can after buying it. It can then be used for any of the popular cold dishes given here. FISH PASTIES (serves four) Ingredients: 6 oz. pastry, 8 oz. white cooked fish, flaked, 4 oz. cooked diced potato, 2 level tablespoons chopped onion, 1 level teaspoon salt, 1/4 level teaspoon pepper, white sauce. Method: Roll the pastry into 6 in. circles. Mix the fish with the other ingredients and if necessary a little white sauce, and pile a quarter of the mixture on each piece of pastry.