- 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.
- 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.
Cooks’ notes: Topping can be made 1 day ahead and chilled, covered.
Half of dish can be baked in 10 (6- to 8-ounce) ramekins for children (with remaining half baked in a 2-quart baking dish for adults).
Recipe by Gina Marie Miraglia Eriquez, Gourmet; photo by Roland Bello.