01 - Preheat your oven to 400°F. Line a baking sheet with parchment paper.
02 - In a bowl, combine the diced butternut squash with olive oil, salt, and black pepper. Toss to coat evenly. Spread the seasoned squash in a single layer on the prepared baking sheet. Roast for 25 to 30 minutes, or until the squash is tender and exhibits slight caramelization.
03 - While the squash is roasting, bring a large pot of salted water to a rolling boil. Add the elbow macaroni or short pasta and cook according to package directions until just al dente. Drain the pasta and set aside.
04 - Once the butternut squash is tender, transfer it to a blender or food processor. Add 1/2 cup of milk and process until a completely smooth puree is achieved.
05 - In a large saucepan, melt the unsalted butter over medium heat. Whisk in the all-purpose flour and cook for 1 minute, stirring constantly, to form a roux.
06 - Gradually whisk the remaining 1.5 cups of milk into the roux. Continue to cook, stirring, for 2 to 3 minutes until the sauce has slightly thickened.
07 - Stir the pureed butternut squash into the thickened milk mixture. Add the grated cheddar cheese, Gruyère or Parmesan cheese, ground nutmeg, and smoked paprika (if using). Cook, stirring frequently, until the cheeses are fully melted and the sauce is uniformly smooth. Season with salt and pepper to your preference.
08 - Add the drained, cooked pasta to the cheese sauce. Gently toss until every piece of pasta is evenly coated.
09 - If desired, preheat the broiler. In a small bowl, combine the panko breadcrumbs with the melted butter. Sprinkle this mixture evenly over the pasta in a suitable baking dish. Broil for 2 to 3 minutes, or until the topping is golden brown and crisp.
10 - Garnish with fresh chopped parsley and serve the butternut squash mac and cheese hot.