Boil the octopus in salted water with 1 whole onion until soft. It'll take a few hours. Mine took about 2 hours or more on medium-high heat. I didn't really keep track of the time however. I tested the softness of the octopus with a toothpick.

Remove the octopus from the water when done and set aside or if making ahead, place in the fridge once cooled. Drain the water over a deep bowl and remove any lumpy, onion bits from the water using a sieve. It makes an excellent fish stock which can also be frozen until needed.

In the meantime, cook the potatoes whole with skins on until fully cooked through. Drain the potatoes, allow to air dry for a few minutes. Then using the back of a spoon squash each potato until it pops slightly but still intact and add the potatoes to a ovenproof tray. Gently toss in olive oil and season with salt.

Transfer to a preheated oven and bake until crispy and browned on the outside. Turn a few times.

To make the sauce, heat the olive oil over medium heat and add the onion and fry for 3-5 minutes or until softened, then add the garlic and coriander and continue to fry for another 3-5 minutes. Don't let the onion or garlic burn. Set aside until needed, it can be reheated if required.

Heat a grill pan over medium-high heat. Cut the octopus into single tentacles and coat in olive oil then char the octopus for a couple of minutes on each side (coal works best but a grill pan will do just fine).