Preheat oven to 375°. Line a baking sheet with foil or parchment paper.

Toss two-thirds of the squash with oil and season with salt and pepper. Roast for 20 minutes, or until mostly done. The squash will continue to cook in the mac and cheese.

With the remaining squash, add to a microwave-safe bowl with ⅓ cup water and cover with plastic wrap. Microwave on HIGH for 8 minutes, or until very soft. Drain and mash with a fork.

Cook pasta according to package directions.

In a large saute pan, melt 2 Tablespoons butter over medium heat. Add onion and cook until softened, about 5 minutes. Add garlic and sage leaves and cook for an additional minute. Season with salt and pepper.

Add the remaining butter and let melt. Stir in flour and dry mustard. Stir for one minute, or until it forms a thick paste.

Pour in half-and-half and milk a little at a time, whisking constantly. Cook until the sauce has come to a bubble and is thick. Remove from heat.

Add 2 cups cheddar and half of the Parmesan cheese and stir until melted and the sauce is smooth.

Add the drained pasta, along with the roasted and mashed squash to the sauce. Mix to combine. Taste and add salt and pepper as needed.

Pour into a 9x13 pan that has been sprayed with cooking spray.

To make the topping, melt butter in a small saute pan over medium-high heat. Add breadcrumbs and cook until toasted, about 3 minutes.

Sprinkle the breadcrumbs evenly over the macaroni and cheese. Top with remaining cheese. Bake for 30 to 40 minutes, or until golden brown and bubbling. Garnish with sage leaves.