Heat oven to 450°. Line unpricked pastry shell with a double thickness of heavy-duty foil. Bake for 8 minutes. Remove foil; bake 5 minutes longer. Cool on a wire rack. In a saucepan, combine sugar and cornstarch. Stir in raspberries; bring to a boil over medium heat. Boil and stir for 2 minutes. Remove from heat; cool for 15 minutes. Spread into shell; refrigerate. In a mixing bowl, beat cream cheese, sugar and vanilla until fluffy. Fold in whipped cream. Carefully spread over raspberry layer. Cover and refrigerate for at least 1 hour. To make topping, melt chocolate and butter together; cool for 4 to 5 minutes. Pour over filling. Cover and chill for 2 hours. Store in refrigerator. Yields 6 to 8 servings.