Bring a large pot of water to a boil and preheat the oven 425°F.
Toss the onions, butternut squash, and sage with olive oil, salt, and pepper. Place on a sheet tray and roast in the oven until golden in color.
Separately, heat the chicken broth in a large skillet on medium heat. Once the squash is done, add the broth and 1/2 of the squash to a blender. Combine the sauce and remaining squash in the large skillet.
Cook the pasta according to the package directions. Before draining, reserve 1/2 cup of the cooking liquid and set aside.
Drain the pasta and combine with the sauce. If the sauce is too thick, dilute with a bit of the reserved cooking water.
Remove the skillet from the heat and fold in the butter until its completely incorporated, then top with Parmigiano cheese and pumpkin seeds.
