For the Thai sauce:
* Optional for octopus cooking:
For the Thai sauce: first prepare the fish broth. Put the piece of fish in a pot with one liter of water (4 cups), together with 1 onion and 2 carrots. Boil for 20–30 minutes, then grind everything, strain, and set the broth aside. Put the oil, ginger, and sliced leeks in the blender. Blend well. Add the fish broth, coconut milk, lemon zest, and season. Blend again, strain, and set aside.
For the carpaccio, there are two options: getting a store-bought carpaccio or cooking the octopus.
Octopus cooking: put plenty of water in a large pot and add onion, celery, carrot and pepper grains. Bring to a boil and grabbing the octopus by the head, submerge the tentacles in boiling water for a few seconds, then take out and repeat the process until all the tentacles have curled up (should be 4 or 5 immersions). Finally submerge the entire octopus and allow to cook for 90 minutes until tender and cooked. With a sharp knife, slice the tentacles as thinly as possible.
To serve, place the octopus slices in a plate and spread the Thai sauce, add blueberries in halves, capers and a dash of olive oil on top. Sprinkle some freshly ground pepper and serve.