1. Preheat oven to 375°F. Line a baking sheet with aluminum foil. Place squash on baking sheet.
2. Bake 50 to 60 minutes, or until a knife can easily pierce squash; let cool until able to handle, then cut in half. Scoop flesh from squash halves; discard skin. Mash squash and set aside.
3. In a medium saucepan over medium heat, melt margarine. Whisk in flour, salt, and pepper until combined. Add milk, whisking until smooth. Cook until thickened and bubbly, stirring often. Add mozzarella and Cheddar cheeses and whisk until cheeses are melted. Stir in squash and add pasta; stir until coated.
4. Coat an 8-inch square baking dish with cooking spray. Place mixture in baking dish and top with muenster cheese slices.
5. Bake 25 to 30 minutes, or until cheese is golden and casserole is bubbly.
Recipe and Image from the Mr. Food Test Kitchen
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