Place the octopus in a pot of cold water, bring to boiling point and cook for one hour. When it is tender, let it cool in the cooking water: this is the secret to keeping it soft. Peel it, rinse it and cut it into pieces.
In the meantime, put the potatoes in cold water with their skins on, bring to the boil and cook for half an hour; peel and dice.
Clean the artichokes, removing hard outer leaves and inner choke, putting them in cold water with lemon juice after cleaning. Boil them in salted water until tender.
Combine the diced potatoes, wedges of artichoke, octopus cut into pieces, sliced scallion and capers with salt rinsed off in a salad bowl.
Dress with a vinaigrette dressing made with olive oil, salt, pepper, lemon juice and chopped parsley.