
Preheat oven to 425°F. Line a large baking sheet with parchment. Place the butternut squash, onions and garlic on the baking sheet. Drizzle with olive oil and season with salt and pepper. Roast until squash is lightly caramelized and golden, about 30 minutes.
While the butternut squash is roasting, cook the pasta in a pot of salted water according to package instructions until al dente. Drain, reserving ½ cup of the cooking liquid.
Transfer the roasted butternut squash to large saucepan. Add the vegetable broth, milk and pasta water, and use an immersion blender to blend until smooth.
Add the cooked pasta to the butternut squash sauce and toss to combine. Serve warm with grated parmesan cheese and chopped parsley, if desired.