Wash the octopus thoroughly under the cold running water. Carefully work through its tentacles to wash off the sand.
Using a 12-quart stock pot, put in roughly chopped celery, carrot, onion, smashed garlic cloves, herbs, bay leaves, ½ cup vinegar, ¼ cup of salt (the water should taste like sea, salty) and peppercorns. Fill the pot with enough water to cover the octopus completely and bring to a boil.
Place a second small pot with just plain water next to the 12-quart pot and bring to a boil. Holding the octopus with tongs dunk it slowly for a few seconds 7 times in a row into a small pot with plain boiling water until its tentacles have curled up.
Transfer the octopus into the 12-quart pot, bring it to boil again then lower the temperature and simmer for 50-60 min. Make sure that the octopus is completely covered by water. Do not let it boil.
Meanwhile, using a small paring knife and scissors cut off the upper third of an empty 1 liter clear plastic bottle and make 6 small holes on its bottom. Put it aside.
Using a slotted spoon or a spider transfer the octopus to the cutting board. Let it cool slightly.
When the octopus is cool enough to handle cut off the head and slice it in half. Cut the body in half and slice off each tentacle.
Take a small bowl or dish and place the cut out plastic bottle in it so that the excess liquid could drain through the holes into the bowl.
Place the tentacles along the inner walls of the plastic bottle with the suction cups facing out. Fill the center of the bottle with the remaining octopus and head pieces. When the process is complete use a glass bottle of water, press by placing it right on top of the octopus inside the plastic bottle (make sure you clean the glass bottle with soap and water and pat dry it thoroughly before pressing it on top of the octopus).
The final assembly has to be placed in the fridge for at least 6 hours. Put it on the bottom shelf and if possible use the shelf above to press down on the glass bottle to further increase the pressure on the octopus. Another option is to cut the edges of the plastic bottle vessel vertically down to the level of the octopus meat. Fold the cut edges on top of the octopus, wrap it in a plastic wrap and put it in the fridge with a weight on top to compress the octopus.
The final product should be a compressed into a cylindrical shaped mass of octopus meat that looks like thick salami. It’s important to create as much weight pressure on top of the octopus as possible; its own juices will act as gelatin and will help to hold the cylindrical shape. This recipe can be made 1-2 days in advance.