Ingredients

• 8 tablespoons (1 stick) unsalted butter, plus more for dish
• 6 slices good white bread, crusts removed, torn into ¼- to ½-inch pieces
• 5.5 cups milk
• 0.5 cup all-purpose flour
• 2 teaspoons salt
• 0.25 teaspoon freshly grated nutmeg
• 0.25 teaspoon freshly ground black pepper
• 0.25 teaspoon cayenne pepper, or to taste
• 4.5 cups grated sharp white cheddar cheese (about 18 ounces)
• 2 cups grated Gruyere cheese (about 8 ounces) or 1 ¼ cups grated Pecorino Romano cheese (about 5 ounces)
• 1 pound elbow macaroni

Instructions

1. Preheat oven, prep dish, and melt butter: Heat oven to 375°F. Butter a 3-quart casserole dish; set aside. In a small saucepan over medium heat, melt 2 tablespoons butter.
2. Butter breadcrumbs: Place bread in a medium bowl. Pour butter into bowl with bread, and toss. Set breadcrumbs aside.
3. Heat milk: In a medium saucepan set over medium heat, heat milk.
4. Melt remaining butter and whisk in flour: Melt remaining 6 tablespoons butter in a high-sided skillet over medium heat. When butter bubbles, add flour. Cook, whisking, 1 minute.
5. Add hot milk and whisk until sauce is thick: While whisking, slowly pour in hot milk. Continue cooking, whisking constantly, until the mixture bubbles and becomes thick.
6. Stir in cheeses and seasonings: Remove pan from heat. Stir in salt, nutmeg, black pepper, cayenne pepper, 3 cups cheddar cheese, and 1 1/2 cups Gruyère or 1 cup Pecorino Romano; set cheese sauce aside.
7. Cook macaroni: Fill a large saucepan with water; bring to a boil. Add macaroni; cook 2 to 3 minutes less than manufacturer's directions, until the outside of pasta is cooked and the inside is underdone. Transfer macaroni to a colander, rinse under cold running water, and drain well.
8. Add macaroni to sauce: Stir macaroni into the reserved cheese sauce
9. Transfer to prepared dish and top with cheese and breadcrumbs: Pour mixture into prepared dish. Sprinkle remaining 1 1/2 cups cheddar cheese, 1/2 cup Gruyère or 1/4 cup Pecorino Romano, and breadcrumbs over top.
10. Bake: Bake until browned on top, about 30 minutes. Transfer dish to a wire rack to cool 5 minutes; serve hot.