Heat olive oil in a large skillet over medium-high heat. Add Italian sausage and cook, breaking it apart, until browned. Remove sausage and set aside, leaving rendered fat in the skillet.

Add chopped onion to the skillet and sauté until softened, about 5 minutes. Stir in minced garlic and cook for another minute until fragrant.

Add diced butternut squash (if using) and chicken broth to the skillet. Bring to a simmer, then reduce heat, cover, and cook until squash is tender, about 10-15 minutes. If using butternut squash puree, add it after the garlic along with the broth.

Pour in the heavy cream and bring the sauce to a gentle simmer. Meanwhile, cook the gnocchi according to package directions in a separate pot of salted boiling water until they float to the surface (usually 2-3 minutes). Drain well.

Add the cooked gnocchi, cooked sausage, baby spinach, and grated Parmesan cheese to the skillet with the sauce. Stir gently until the spinach wilts and everything is well combined and heated through. Season with salt and black pepper to taste. Serve immediately.