INGREDIENTS
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1/2 cup (1 stick) unsalted butter, plus more, softened, for baking dish
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6 slices good-quality white bread, trimmed of crusts and torn into 1/4- to 1/2-inch pieces
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5 1/2 cups milk
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1/2 cup all-purpose flour
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2 teaspoons coarse salt
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1/4 teaspoon freshly grated nutmeg
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1/4 teaspoon freshly ground pepper
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1/4 teaspoon cayenne, or to taste
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4 1/2 cups grated sharp white cheddar (about 1 1/4 pounds)
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2 cups grated Gruyere (about 8 ounces)
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1 pound elbow macaroni