Macaroni and Cheese with Butternut Squash

INGREDIENTS

• 1 small butternut squash (about 1 pound), peeled, seeded, and cut into 1-inch cubes (about 3 cups)
• 1 cup homemade or low-sodium canned chicken stock, skimmed of fat
• 1 1/2 cups nonfat milk
• Pinch of freshly grated nutmeg
• Pinch of cayenne pepper
• 3/4 teaspoon coarse salt
• Freshly ground black pepper
• 1 pound elbow macaroni
• 4 ounces extra-sharp cheddar cheese, finely grated (about 1 cup)
• 4 tablespoons Parmesan cheese, finely grated (1 ounce)
• 2 tablespoons fine breadcrumbs
• 1 teaspoon olive oil
• Olive-oil, cooking spray
• 1/2 cup part-skim ricotta cheese