PREHEAT oven to 400°F. Mix sweet potatoes, sugar, milk, butter, flour, spices, eggs and vanilla in large bowl until blended.
POUR into pastry shell. (Shell will be quite full; filling will not rise over sides.)
BAKE 30 to 35 minutes or until top is puffed and browned. (Filling will be soft, but will set while cooling.) Cool on wire rack at least 2 hours. Serve each slice with 2 tablespoons whipped topping.