Start by preheating the oven to 425 F and line a large baking sheet with parchment paper.
Line your squash cubes on the baking sheet, along with your onions, shallot, and garlic cloves.
Toss all of your veggies with olive oil, salt, and pepper.
Roast for about 30 minutes, until the squash is fork tender.
While the squash is cooking, prepare the pasta. Boil a pot of salted water and cook the pasta until its al dente. Drain when done, and make sure to reserve 2/3 cup of pasta water for later.
Next, add the roasted butternut squash to a large pot on the stove, along with the broth, milk, and lemon juice.
Then, use an immersion blender to blend everything together until it's perfectly creamy. If you don’t have an immersion blender, you can do this in smaller batches in a regular blender, and then just return it to the pot once finished.
Add the pasta to the pot with the sauce, and toss to coat it well, making sure to add in the pasta water as well.
Taste, and adjust the seasonings as needed.
Finally, plate your pasta, sprinkle generously with the parmesan cheese, serve, and enjoy!