Preheat your oven to 400°F (200°C). Peel, seed, and dice the butternut squash. Toss with olive oil, salt, and pepper, then roast for 20–25 minutes until tender and caramelized.

In a large skillet, heat olive oil over medium-high heat. Add Italian sausage, breaking apart, and cook for 6–8 minutes until browned. Remove from skillet and set aside.

In the same skillet, reduce heat to medium and add chopped onion. Sauté for about 5 minutes until translucent. Add minced garlic and cook for 1 more minute.

Stir in baby spinach and wilt for 2–3 minutes until bright and tender.

In a large pot, boil salted water. Cook pasta according to package instructions until al dente, about 8–10 minutes. Reserve ¼ cup pasta water, then drain.

Blend the roasted squash with reserved pasta water if a smoother sauce is desired; otherwise, add it directly.

Combine roasted squash with spinach, onion, and sausage in the skillet. Pour in heavy cream, season with sage, salt, and pepper.

Add cooked pasta, toss to coat in sauce, and adjust consistency with reserved pasta water. Mix in grated Parmesan cheese.

Serve the pasta garnished with more Parmesan and optional red pepper flakes.