4-5 pounds frozen octopus
Kombu (Japanese kelp)
2 oz sea salt
Daikon (Japanese radish)
1. Put on a pot of water, about a gallon, and add a good sized piece of kombu and about 2 oz of sea salt. Bring to a boil.
2. Thaw octopus in cold water, then drain well.
3. Knead the octopus with a large amount of fresh grated/chopped daikon radish and sea salt. What this does is to clean off any slime, and it also tightens the skin up just a bit. While doing that, turn the head inside out and check for any leftover viscera. Remove any that's found, then return the head sac to it's correct shape.
4. Using a fork, dunk the octopus into the boiling water a few times until the tentacles curl up. Lower the heat a bit, and then simmer the octopus for about 5-10 minutes. After that turn the heat off and cover the pot.
5. Let the octopus cool in the liquid for at least an hour, then into the fridge the whole thing goes. Overnight is great if you can manage it, it's the slow cooling that tenderizes it. Remove the octopus from the water and let it dry a bit. Slice on an angle, then serve as you like.
You'll probably find the skin around the head to be very tough. This skin is better off discarded. The very top of the tentacles where they conjoin into the head will probably also have a gelatinous layer right under the skin that's not too edible either so should be removed as well.
2009/03/16 From http://www.sushifaq.com/recipes/octopus-for-sushi.htm