Combine cheeses, eggs, parsley, salt, and pepper. Fill each shell with about 2 tbsp of the cheese mixture. Spread a thin layer of sauce on the bottom of a 13 x 9 inch baking pan. Place shells in pan, cover with remaining sauce. Sprinkle with additional parmesan or mozzarella cheese, if desired. Cover with aluminum foil, bake at 350 degrees for about 35 minutes, or until hot and bubbly.