Preheat oven to 350 degrees F (175 degrees C). Beat together the cream cheese and the sugar, add the pumpkin and the spices. Beat in eggs one at a time. Add salt. Beat until creamy. Pour the batter evenly into the two pastry shells. Bake at 350 degrees F (175 degrees C) for 50 minutes or until the knife inserted in the center comes out clean. Let cool then top with whipped topping, if desired.