01 - Combine olive oil and butter in a large, deep skillet or Dutch oven over medium heat, allowing the butter to melt and the mixture to become fragrant.
02 - Add the finely chopped onion with a pinch of salt. Cook for 3 to 4 minutes until the onion is softened and translucent.
03 - Stir in minced garlic and chopped sage. Sauté for 1 minute, stirring constantly to release the aromas.
04 - Introduce the butternut squash cubes. Cook for 2 to 3 minutes, lightly stirring, until the squash begins to soften at the edges.
05 - Pour in vegetable broth and water. Increase heat to bring to a gentle simmer.
06 - Add the pasta, nutmeg, and a generous pinch of salt and freshly ground black pepper. Stir thoroughly to combine.
07 - Cover and cook, stirring occasionally, for 12 to 15 minutes, or until both pasta and squash are tender and most of the liquid has been absorbed.
08 - Reduce heat to low. Stir in heavy cream and grated Parmesan. Mix gently until the sauce becomes smooth and coats the pasta evenly. Adjust seasoning if necessary.
09 - For an ultra-creamy consistency, gently mash some of the cooked squash with the back of a spoon, blending it into the sauce.
10 - Plate the pasta warm, finishing with additional Parmesan and whole sage leaves (pan-fried in butter if desired) as a garnish.