Preheat oven to 425 F. Line a 10″ pie plate with pastry. Place raspberries in a bowl. Combine sugar and cornstarch. Toss gently with rasberries, and place in pie shell. Sprinkle with lemon juice and dot with butter. Cover with pastry. If desired, brush top pastry with 1 tablespoon of light cream and sprinkle with 1 tablespoon of sugar. Bake for 15 minutes at 425F. Reduce heat to 350F and bake for 35 minutes more, or until golden.