A recipe for a casserole of macaroni, white sauce, and grated yellow cheese was recorded in the Boston Cooking School Cookbook in 1896, and Americans have enjoyed this homespun classic ever since. . .The sum of all these [ingredients] bakes into a truly memorable dish with a crisp, browned top that contrasts beautifully with the creamy molten center. Nothing from a boxed mix can hold a candle to that.
1. Preheat oven to 375°F. Butter a 3-quart casserole dish. Place bread in a medium bowl. Melt 2 tablespoons butter in a small saucepan over medium heat; pour into bowl with bread, and toss to coat.
2. Heat milk in a medium saucepan over medium heat. Melt remaining 6 tablespoons butter in a high-sided skillet over medium heat. Add flour to make a roux, and cook, stirring, 1 minute (do not let brown). While whisking, gradually pour in hot milk. Continue cooking, whisking constantly, until the mixture bubbles and thickens. Remove the pan from heat. Stir in salt, nutmeg, pepper, cayenne, 3 cups cheddar, and 1 ½ cups Gruyère.
3. Cook the pasta in a large pot of boiling water 2 to 3 minutes less than the manufacturer's directions. Drain macaroni, rinse under cold running water, and drain again. Stir macaroni into cheese sauce.
4. Pour mixture into prepared dish. Sprinkle evenly with remaining 1 ½ cups cheddar and ½ cup Gruyère, then top with bread pieces. Bake until heated through and topping is browned, about 30 minutes. Transfer to a wire rack to cool 5 minutes before serving.