Preheat the oven to 400 F. Cut the squash in half and remove the seeds with a spoon. Line a baking sheet with parchment paper. Place the squash halves on the baking sheet cut side up. In each squash half put one tablespoon of butter and two sage leaves.
Bake for about one hour or until flesh is soft when pierced with a knife tip. Set aside to cool for about 15 minutes. Scrape the flesh out with a fork to get spaghetti like strands.
Heat the remaining 3 tablespoons of butter in a large frying pan over medium heat. When the butter is melted, add the remaining sage leaves. After a few minutes add the squash and mix. Cook for about 3-5 minutes. Season with salt and pepper to taste. Serve in the hollowed out squash skin or in a bowl and sprinkle with Parmigiano-Reggiano cheese.