Preheat oven to 425.

Place the squash in the oven in a baking dish. Add a generous splash of water to the pan. Roast for 25-35 minutes. When you can easily scoop the flesh with a spoon it is done. The longer the squash is roasted the softer it will become.

While the squash roasts, bring a large pot of water to a boil. Melt the butter in a saucepan over medium heat. Sprinkle in the flour, while whisking constantly. When it begins to color slightly and/or smells a bit nutty, it is time to add the warm milk. Drizzle it in slowly while whisking; it will begin to thicken. Reduce the heat, add the salt, black pepper and nutmeg. Whisk periodically to prevent the bottom from burning.

When the squash is done roasting, add the pasta to the boiling water. Place the squash in the fridge or outside if it is chilly, to cool faster.

When you can handle the squash* scoop it into a food processor or blender. Add as much of the white sauce as needed for it to blend smoothly. Alternatively, push it through a food mill or use a potato masher to smooth the squash. Whisk the squash puree with the remaining white sauce and just over half of the shredded cheese.

When the pasta is done, drain it well, and combine with the white sauce. Dump it into a baking dish. Sprinkle on the remaining shredded cheese and finish with the breadcrumbs.

Bake in the oven at 375 for 20-30 minutes until bubbly. If baking after the Mac n Cheese has cooled, cover with foil and bake 10-20 more minutes.

*You will want approximately the same amount of squash as white sauce. The ratio for four servings will be:
1/2 pound pasta to 1 1/2 cups cooked squash to 1 1/2 cups white sauce. Although, feel free to approximate the amount of squash and sauce as this dish is very forgiving. Any extra squash freezes beautifully, too.