Preheat your oven to 400°F (200°C). Toss cubed butternut squash with olive oil, salt, and pepper. Spread on a baking sheet and roast for 20-25 minutes until tender.

In a large skillet, heat olive oil over medium heat. Cook Italian sausage until browned. Add onion and cook until softened, then stir in garlic and spinach until spinach wilts.

Boil salted water in a large pot. Add pasta and cook until al dente, reserve ¼ cup pasta water, then drain.

In the skillet, combine roasted squash, pasta, heavy cream, and Parmesan. Stir over low heat, adding reserved pasta water to reach desired sauce consistency.

Serve garnished with additional Parmesan and red pepper flakes, if desired.