Mac and Cheese
For topping1/2 stick unsalted butter
2 cups panko (coarse Japanese bread crumbs) or 3 cups coarse fresh bread crumbs (from 6 slices firm white sandwich bread)
1/4 pound coarsely grated extra-sharp Cheddar (1 1/2 cups)
1/2 cup grated Parmigiano-Reggiano
For macaroni and sauce
1 stick unsalted butter
6 tablespoons all-purpose flour
5 cups whole milk
1 pound coarsely grated extra-sharp Cheddar (6 cups)
1/2 cup grated Parmigiano-Reggiano
1 pound elbow macaroni
Make topping:
Preheat oven to 400°F with rack in middle.
Melt butter, then stir together with panko and topping cheeses in a bowl until combined well.
Make sauce:
Melt butter in a heavy medium saucepan over medium-low heat and stir in flour. Cook roux, stirring, 3 minutes, then whisk in milk. Bring sauce to a boil, whisking constantly, then simmer, whisking occasionally, 3 minutes. Stir in cheeses, 2 teaspoons salt, and 1/2 teaspoon pepper until smooth. Remove from heat and cover surface of sauce with wax paper.
Make Macaroni:
Cook macaroni in a pasta pot of boiling salted water (2 tablespoons salt for 4 quarts water) until al dente. Reserve 1 cup cooking water and drain macaroni in a colander. Stir together macaroni, reserved cooking water, and sauce in a large bowl. Transfer to 2 buttered 2-quart shallow baking dishes.
Sprinkle topping evenly over macaroni and bake until golden and bubbling, 20 to 25 minutes.