Preheat oven to 400°F (200°C). Cube the butternut squash, toss in olive oil, and roast for 20-25 minutes until tender.

In a skillet, heat olive oil, add Italian sausage, and cook until browned, about 5-7 minutes. Remove and set aside.

Sauté chopped onion in the same skillet for about 5 minutes. Add minced garlic and cook for 1 minute.

Add baby spinach to the skillet and sauté for 2-3 minutes until wilted.

Boil salted water and cook pasta according to package instructions until al dente. Reserve a cup of pasta water before draining.

Optionally, blend the roasted squash for a smooth sauce. Return to skillet with sautéed ingredients and sausage.

Add heavy cream, sage, salt, and pepper to the skillet. Simmer for 2-3 minutes to combine flavors.

Mix in the drained pasta and adjust the sauce with reserved pasta water if necessary.

Serve immediately, topped with grated Parmesan and red pepper flakes if desired.