Scrub the mussels and clams well with a stiff brush or pot scourer. Discard any mussel or clam that is open or has a broken shell. Put them in a little water over a low heat and cook just until their shells open. This will make sure that any sand comes out and does not go into your sauce (The shellfish are served in their shells so put small plates on the table for the shells to be discarded as the shellfish are eaten).
Very small squid are usually served whole. If using larger squid, cut the sack into rings, remove and discard the head and the hard part in the of the ring joining the tentacles, and cut the rest into small pieces.
Heat the extra virgin olive oil in a large pan and add the chopped garlic and the chili pepper. When the garlic begins to turn colour add the small squid and the prawns. After 5 minutes add the mussels and the clams. Season with salt and cook for 10 minutes.
The spaghetti should be cooked for only half the time stated in the packet instruction. Drain the pasta and very quickly mix it with the hot shellfish sauce and chopped Italian parsley. Have a double layer of aluminum foil ready on backing sheet. Put the spaghetti mixture in the middle and fold over the foil, making sure all the folds are thightly closed to prevent any steam escaping.
Cook in a hot oven, 425°F/220°C for 7 minutes.
Carry the foil parcel to the table. Open, stir well with a wooden fork and serve from the foil. The aroma that comes out in the cloud of steam has to be experienced to be believed.