1 medium butternut squash (about 1-1/4 pounds), peeled and cut into 1/2-inch cubes
1 medium yellow onion, cut into 1-inch pieces
2 tablespoons olive oil
2 teaspoons kosher salt, plus salt for pasta water
1 teaspoon ground black pepper, divided
1 pound rotini pasta
1 (5 oz) wedge Stella Parmesan Cheese, shredded
3 sage leaves, roughly chopped, plus additional leaves for garnish, if desired
1 cup chicken broth
1/2 cup heavy cream
1 teaspoon apple cider vinegar
Pinch red pepper flakes
Preheat oven to 350 degrees F. Place walnuts on rimmed baking pan. Transfer to oven and bake 8 minutes. Transfer walnuts to small bowl. Leave oven on.
Add squash and onion to same rimmed baking pan. Drizzle with oil and sprinkle with salt and 1/2 teaspoon black pepper; toss until well combined. Transfer to oven and bake 15 minutes or until squash is very tender.
Meanwhile, in large pot of boiling salted water, cook pasta according to package instructions.
Set aside 1/2 cup cheese for garnish. Add remaining cheese, 3 sage leaves, broth, cream, vinegar, red pepper flakes, walnuts, squash mixture and remaining 1/2 teaspoon black pepper to blender and blend until smooth.
Transfer sauce to large pot. Heat over medium heat 3 minutes, stirring occasionally. Drain pasta and add to pot with sauce. Cook 2 minutes or until warmed through, stirring frequently.
Let pasta stand 5 minutes before serving (sauce will continue to thicken). Serve pasta garnished with reserved cheese and additional sage leaves, if desired.