Roast butternut squash in a foil covered baking dish with an inch of water at 350° for 45 minutes or until tender. Let cool until it’s easy to handle.

Scrape the butternut squash from the peel and place in a blender with ½ cup water; blend until smooth.

Brown chicken sausage in a large sauté pan. Remove to a plate lined with paper towels.

Cook pasta according to package directions. Reserve 1 cup pasta water.

While pasta is cooking, melt butter in the sauté pan. Sauté onions, celery, and carrots over medium-high heat. Add garlic and cook 1 minute more. Stir in Italian seasoning, red pepper flakes, salt, and pepper. Mix in browned chicken sausage.

Add pureed butternut squash, and reserved pasta water a little at a time to thin out the sauce to desired consistency. Mix in baby spinach and parmesan cheese. Add additional salt and pepper to taste.

Pour sauce over pasta and toss to combine. Serve with additional parmesan cheese.