Lightly brush the rim of the pastry shell with a little cream. Starting at the outside edge of the pie, place the pastry stars in a circular pattern on top of the blackberries. Brush the pastry stars with cream, making sure the cream does not pool. Sprinkle with a little sugar, if desired. Cover with plastic wrap and place in the refrigerator while you preheat the oven to 425 degrees F (220 degrees C) and place the oven rack in the lower third of the oven.