Bring a large pot of water to a boil. Fill a large saucepan with water and bring it to a boil over high heat. You can get this started while you peel and chop the squash.
Peel and chop the squash. Peel the butternut squash, remove the seeds, and cut the flesh into roughly 1-inch cubes. You'll need 6 heaping cups of chopped squash for this recipe.
Boil the squash. Add the cubed squash to the boiling water and cook for about 10 minutes, or until fork-tender. A fork should easily slide through the cubes without resistance.
Drain the squash. Remove the saucepan from the heat, turn off the burner, and carefully drain the squash in a colander. Return the cooked squash to the saucepan.
Blend the squash. Add the vegetable broth to the saucepan. Use an immersion blender to blend the squash and broth until completely smooth. The mixture will be very thick, with a consistency similar to baby food puree. Make sure there are no remaining chunks of squash.
Add the heavy cream. Place the saucepan back on the stove over medium heat and stir in the heavy cream until fully incorporated. Bring the sauce to a gentle simmer, stirring occasionally.
Add the seasonings and Parmesan. As soon as the sauce begins to bubble, turn off the heat. Stir in the shredded Parmesan, salt, garlic powder, and sage until the cheese is melted.
Serve and enjoy! This recipe makes about 4 cups, enough to coat 1 pound of cooked pasta. Toss the sauce with pasta while it's warm, as it will thicken even more as it cools. Enjoy!