Why on earth are there more than 300 different pasta shapes ? Some people may think that they all have the same taste but those in the know recognise that each pasta is made for a special recipe, for a special sauce.
"Penne rigate" (striped feather as Italians call them) are perfect for gratins. Just add some bechamel sauce with parmesan to the cooked pasta. Transfer to an oven-proof dish and bake until browned.