Wash the soaked cod skins, place in water and bring to the boil. Turn the heat down to the minimum and simmer until reduced to one quarter of the original volume. Strain and season with salt. Set aside. Wash the parsley in cold water. Dry and break into pieces. Cover with the olive oil and leave to macerate overnight. Next day, place in the blender with the salt, garlic and cayenne pepper. Blend until a fine texture is obtained, then strain. Check the seasoning. Chill. Soak the sheets of gelatin in cold water and drain. Heat the cod stock in a pan and, when bubbling, add the agar-agar and on-dashi and mix until dissolved. Remove from the heat. Leave to cool by just a few degrees and add the gelatin.
When it is cool enough for you to insert your finger, add the pistou and mix in carefully. Then add the oil in the same way, beating to maintain the emulsion. Heat the olive oil to 65ºC / 149ºF. Submerge the pieces of cod in the oil and leave to cook for 3 or 4 minutes. Drain on kitchen paper. Heat the pilpil sauce to between 45ºC / 113ºF and 50ºC / 122ºF.
Preparation by: Andoni Luis Aduriz