Prepare the vegetables for boiling the octopus. Bring a pot of water to a boil with the vegetables and peppercorns. Dip the octopus into the boiling water 2 or 3 times to curl the tentacles.

Prepare a plastic bottle by cutting off the top and poking small holes in the bottom. This will help drain the octopus liquid.

Once the octopus is cooked, leave the tentacles whole and cut off the head and other parts. Layer the octopus pieces in the bottle, pressing down firmly to remove as much cooking liquid as possible.

When all the octopus is in the bottle, fold the edges of the bottle over and press down. Cover completely with plastic wrap. Place the bottle in a container (to catch any liquid) and refrigerate in the coldest part of your fridge for 24 hours.

After 24 hours, cut open the plastic bottle and slice the octopus carpaccio thinly. If it isn't firm enough, freeze for 1 hour to help it set, then slice and arrange on a serving platter.

Make the citronette by mixing lemon juice, olive oil, salt, and chopped fresh herbs. Pour over the octopus and let it marinate for 1 hour.

Serve the octopus carpaccio garnished with fennel fronds.