Preheat the oven to 200°C (390°F) and line a baking tray with parchment paper.
Peel the squash, remove the seeds and fibrous parts, and cut the flesh into cubes. Place the cubes on the baking tray, drizzle with olive oil, and toss to coat.
Bake for 20–25 minutes, until the squash is very tender.
Transfer the cooked squash to a blender and blend until you get a very smooth purée.
In a saucepan, combine the plant-based cream, the Jeanne cut into pieces, the pressed garlic, and the nutmeg. Heat over medium heat, stirring, until the Jeanne melts.
Add the squash purée. Mix and let cook over low heat for 2 minutes. Season with salt and pepper. Remove from heat and set aside.
Cook the spaghetti until al dente. Drain, reserving a little of the cooking water.
Immediately pour the squash cream over the pasta and mix. Add a bit of the pasta cooking water to loosen the sauce and achieve a smooth, creamy coating consistency.
Serve the pasta on plates. Top with pieces of Jeanne, roasted hazelnuts, and fresh sage leaves. Enjoy!