01 - Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper. Toss the cubed butternut squash with olive oil, kosher salt, and black pepper. Spread the seasoned squash in a single layer on the prepared baking sheet. Roast for 20-25 minutes, or until the squash is tender and shows signs of light caramelization.
02 - While the squash is roasting, cook the elbow macaroni or pasta shells according to the package directions until al dente. Drain the pasta thoroughly and set aside.
03 - Once the butternut squash is roasted and tender, carefully transfer it to a blender or food processor. Add the vegetable broth and blend until a smooth puree forms. Set this puree aside.
04 - In a large saucepan over medium heat, melt the unsalted butter. Once melted, whisk in the all-purpose flour to create a smooth paste. Cook this roux for 1 minute, stirring constantly.
05 - Gradually whisk the whole milk into the roux, continuing to stir constantly to prevent any lumps from forming. Bring the mixture to a gentle simmer, stirring frequently.
06 - Add the smooth butternut squash puree to the saucepan with the milk mixture. Stir to combine. Incorporate the ground nutmeg, garlic powder, and optional mustard powder. Season generously with salt and freshly ground black pepper to your preference.
07 - Reduce the heat to low. Add the shredded sharp cheddar cheese and Gruyère or mozzarella cheese to the sauce. Stir gently until the cheeses are completely melted and the sauce is velvety smooth.
08 - Add the cooked and drained pasta to the cheese sauce. Stir well to ensure every strand of pasta is evenly coated.
09 - If opting for a baked topping, transfer the sauced pasta to a greased baking dish. In a small bowl, combine the panko breadcrumbs, melted butter, and grated Parmesan cheese. Sprinkle this mixture evenly over the top of the mac and cheese. Bake in the preheated oven at 400°F (200°C) for 12-15 minutes, or until the topping is golden brown and the dish is bubbly.
10 - Serve the Butternut Squash Mac and Cheese hot. Garnish with fresh herbs, if desired, for an added touch of freshness.