Make the aïoli as. If you want to make this in advance, cover it with cling film, making sure the film touches the aïoli and excludes any air. This will stop a skin forming.
Place the palourdes and razor clams in a large bowl of cold water and soak for 10 minutes. Rinse and repeat. This removes any sand from the shells.
Strip the leaves from the parsley and basil and chop or tear. When the shellfish are cooked, sprinkle with the herbs and seasoning and serve with the aïoli.