Cook the frozen octupus(cooking it frozen will make the flesh tender and smooth) in a steam pan for about 20 mn along with the onion;
Meanwhile, boil the potatoes for 15 mn, potatoes should be cooked trough but firm; press the potatoes gently with the palm of your hands on an plate until the skin begins to open.
Remove the octupuss from the pan an cut the legs in pieces about three inches long;
Smash the head cloves without peeling and add them to the olive oil in a baking tray; put the octupus pieces inside the tray add the boiled unpeeled potatoes, add salt and the black pepper and top with some sprigs of fresh parsley. Add some of the cooking liquid, mix all the ingredients and put it in the oven for about 30 mn or until potatoes and octupus look golden and almost caramelised.