Preheat the oven to 200°C/400°F.
Peel the butternut and chop the nose off (the longer/slim part), slice into 1cm slices and set aside.
Then take the ball off the butternut, scoop out the seeds and discard. Chop into small cubes.
Place the cubes along with the garlic and thyme in a pan, cover with boiling water and cook for 15 mins until soft. Drain.
Place the cooked cubes in a food processor and blend along with the crème fraiche, half the Pié d’Angloys and salt and pepper.
Take a medium sized baking dish and start making the gratin. Start with a layer of the puree and then a layer of the sliced butternut, repeat until all the mixture is used.
Pour over the milk and cover the dish with foil, bake in the oven for 45 mins.
Meanwhile, chop half the sage and add to the bread crumbs.
After 45 mins of cooking, remove the foil, top with the bread crumbs and scatter the remaining cheese and sage leaves. Drizzle with olive oil and then bake for a further 20 mins until golden on top.