In a pot of water, boil the plantains, cut in half, until tender.
Meanwhile, wash the octopus thoroughly and rub any grit off the tentacles. Once it is clean, separate the tentacles.
Cook the octopus before anything else: bring a large pot of unsalted water to the boil, lower the octopus in and out three times for a few seconds each, then leave it to simmer. Allow roughly 15 to 20 minutes per kilo, and from 20 minutes onwards test the thickest part of a tentacle with a skewer: it should go in with a little resistance still, not slide through. Take the pot off the heat and let it sit in its own water, covered, for another 15 minutes.
Lay the cooked tentacles on a flat surface and tap them gently with the blunt side of a knife to loosen the fibres.
Put the tentacles in a bowl with the white wine, the spices you like, the thyme, the garlic, salt and pepper. Mix and leave to marinate for at least 20 to 30 minutes.
Once the plantains are done, take them off the heat, peel them and mash them in a bowl. Add the butter, the milk, the parmesan and the sugar. Mix well and taste.
After marinating, sear the octopus in a pan with a little oil for 2 minutes, just to colour it. It is already cooked, so this is only for the outside.
To serve, spoon the purée onto the plate first and arrange the tentacles on top.
Serve straight away.