Cook the macaroni according to package directions until al dente. Drain and set aside.

Heat the butter in a large skillet over medium-low heat. Sauté the thinly sliced onion rings for about 20 minutes until golden and fragrant.

Meanwhile, prepare the butternut squash by removing seeds and skin, then cubing the flesh. Boil the broth and cook the squash for 5-7 minutes until fork-tender.

Drain the squash, reserving 1/2 cup of the broth. Transfer the cooked squash to a blender.

Add the sautéed onions, milk, 1 teaspoon salt, and the reserved broth to the blender with the squash.

Blend until the mixture is completely smooth and creamy, yielding approximately 4 cups of sauce. Combine this sauce with the cooked macaroni and stir well.

Stir in the shredded cheese until it is fully melted and the sauce is creamy. Season with additional salt and pepper to taste. Top with fresh parsley before serving.