Step 1

Arrange a rack in the middle of the oven and heat to 425°F.

Step 2

Toss the cubed squash with the garlic and olive oil in a large bowl and season with ½ teaspoon of the salt and pepper. Transfer the mixture to a rimmed baking sheet and spread into a single layer. Roast until tender and caramelized, about 30 minutes, stirring once halfway through.

Step 3

Remove the squash from the oven and let cool for 10 minutes. Transfer the squash and garlic to a blender or food processor. Add the remaining salt, cream, broth, cheese, and nutmeg, and process continuously until smooth, about 1 minute.

Step 4

Meanwhile, bring a large pot of salted water to a boil. Add the fettuccine and cook until al dente, about 10 minutes or according to package instructions. Reserve 1/2 cup of the pasta water, then drain the pasta. Return the pasta to the pot.

Step 5

Add the Alfredo sauce and toss with the pasta over low heat. If needed, add some of the reserved pasta water, tablespoon by tablespoon, to loosen the pasta and evenly coat it with the sauce. Sprinkle with the parsley and more Parmesan and serve immediately.