Preheat oven to 400°. On a baking sheet, arrange butternut squash chunks in a single layer. Drizzle olive oil over the squash and toss. Sprinkle with salt and black pepper to taste. Roast for 20 to 30 minutes, or until tender, turning once.

While the butternut squash is roasting, cook macaroni according to package directions and drain well. Set aside.

Add butternut squash to food processor or blender and purée until smooth. Add in 1/2 cup of the milk and purée again.

Reduce oven temperature to 350°. Lightly coat a 2-quart casserole dish with nonstick cooking spray.

In a large saucepan over medium heat, melt the butter. Add the flour and nutmeg and cook, whisking constantly, for 2 to 3 minutes, or until just browned. Add the remaining 1 1/2 cups milk and whisk until mixture is smooth. Increase heat to high and bring to a boil while continuing to whisk. After sauce has thickened, reduce heat to low and whisk in butternut squash mixture. Add the cheeses and stir until melted. Add the cooked macaroni to the pan and stir until the noodles are well coated. Season with pepper to taste. Transfer the macaroni to the prepared casserole dish. Sprinkle bread crumbs on top.

Bake for 20 minutes, or until macaroni and cheese is bubbling. Heat under a broiler for 2 minutes, or until bread crumbs are lightly browned. Remove from oven and let rest for 5 minutes. Serve warm.