If an octopus hasn't already been prepared, consult the Great British Chefs video for instructions on how to section an octopus.
The most basic way of cooking octopus is to simmer it in liquid. Fill a saucepan with salted water and bring to the boil. Add the octopus, reduce the heat immediately and simmer gently for 45–60 minutes. It's important that the water is turned down to a gentle simmer once the octopus is in the pan. Cooking it too quickly will result in a rubbery texture.
Judge the tenderness of the octopus by pushing a knife into one of the tentacles; if it easily pushes into the thickest part of the flesh, it's cooked.
Octopus contains a lot of moisture, some of which can be removed by brining or sun-drying to make the flesh more tender before grilling, barbecuing or pan-frying. Without removing some of the moisture from the flesh, the octopus will take on a chewy and rubbery texture.
This step isn't always necessary though – some methods embrace the springy texture of octopus flesh. For example, octopus can be simply marinated and enjoyed in a carpaccio style, used in sushi or deep-fried in a takoyaki batter for an enjoyable, crunchy texture.