When preparing the following pastas in advance (up to six hours), keep them covered and chilled and then let them come to room temperature before baking.
7 Tablespoons unsalted butter
1/4 cup plus 2 Tablespoons all-purpose flour
4 cups milk
1 1/2 teaspoons dry mustard
1/8 teaspoon cayenne, or to taste
1 pound elbow macaroni
3 cups coarsely grated extra-sharp Cheddar cheese (about 12 ounces)
1 1/3 cups freshly grated Parmesan cheese (about 4 ounces)
1 cup fresh bread crumbs
Preheat oven to 350° F and butter a 3- to 4-quart gratin dish or other shallow baking dish.
In a heavy saucepan melt 6 Tablespoons butter over moderately low heat.
Add flour and cook roux, whisking, 3 minutes.
Add milk in a stream, whisking, and bring to a boil, whisking.
Add mustard, cayenne, and salt and pepper to taste and simmer sauce, whisking occasionally, until thickened, about 2 minutes.
In a kettle of salted boiling water cook macaroni until just al dente, about 7 minutes, and drain well.
In a large bowl stir together macaroni, sauce, Cheddar, and 1 cup Parmesan and transfer to prepared dish.
In a small bowl stir together bread crumbs and remaining 1/3 cup Parmesan and sprinkle evenly over macaroni.
Cut remaining 1 Tablespoon butter into bits and scatter over topping.
Bake macaroni in middle of oven 25 to 30 minutes, or until golden and bubbling.