Step 1: Cook the Pasta : Bring a large pot of salted water to a boil. Cook pasta according to package instructions until al dente. Drain and set aside.
Step 2: Cook the Butternut Squash : Option 1 – Boil: Boil cubed squash in water until tender, about 10–12 minutes. Drain and puree in a blender or food processor until smooth. Option 2 – Roast (Optional for richer flavor): Preheat oven to 400°F (200°C). Toss squash with a little olive oil, salt, and pepper. Roast for 20–25 minutes until tender, then puree.
Step 3: Make the Cheese Sauce : In a large saucepan, melt butter over medium heat. Whisk in flour to form a roux and cook for 1–2 minutes. Gradually whisk in milk and pureed squash until smooth and thickened. Stir in Dijon mustard, garlic powder, nutmeg (if using), salt, and pepper. Add cheddar and Parmesan, stirring until melted and smooth.
Step 4: Combine Pasta and Sauce : Add cooked pasta to the cheese sauce, stirring to coat evenly. Pour mixture into a baking dish if planning to bake.
Step 5: Optional Baking : Preheat oven to 375°F (190°C). Mix breadcrumbs with melted butter and Parmesan. Sprinkle over mac and cheese. Bake for 15–20 minutes until topping is golden and crisp.