Place the butternut squash, onions, and garlic on a rimmed baking sheet. Drizzle with olive oil and salt, and toss to coat. Roast until the vegetables are tender and golden brown, about 24-26 minutes.
Meanwhile, bring a large pot of salted water to a boil over high heat. Cook the pasta according to package directions. (If not using broth: Remove 1¼ cups of the pasta cooking water and set aside to reserve.) Drain the pasta, and return it to the pot.
Transfer the roasted vegetables to a blender with the broth (or pasta cooking water) and cottage cheese.
Blend until smooth and creamy, adding as much of the pasta cooking water (or broth, if using) as needed to make a smooth sauce.
Add as much of the sauce to the cooked pasta as you like and toss to coat.
Serve immediately with additional salt, and Parmesan, and/or black pepper as you like.
P.S. You can also make the sauce even creamier by adding a little heavy cream and stirring well.
Notes
Make the sauce up to 5 days ahead of time and store in an airtight container in the refrigerator. Or, you can freeze it for up to a year in a small freezer container.
Store leftover pasta and sauce in an airtight container in the fridge and reheat as you like.
Use frozen or precut vegetables to save on chopping.
Dairy-free: Use white beans in place of the cottage cheese and a little nutritional yeast instead of Parmesan.