1) Heat the oven to 375 degrees. Butter a 3-quart casserole dish; set aside.

2) Place bread pieces in a medium bowl. In a small saucepan over medium heat, melt 2 tablespoons butter.

3) Pour butter into the bowl with bread, and toss. Set the breadcrumbs aside. In a medium saucepan set over medium heat, heat milk. Melt remaining 6 tablespoons butter in a high-sided skillet over medium heat. When butter bubbles, add flour. Cook, stirring, 1 minute.Slowly pour hot milk into flour-butter mixture while whisking. Continue cooking, whisking constantly, until the mixture bubbles and becomes thick.

4) Remove the pan from the heat. Stir in salt, nutmeg, black pepper, cayenne pepper, 3 cups cheddar, and 1 1/2 cups Gruyere. Set cheese sauce aside.Fill a large saucepan with water. Bring to a boil.

5) Add macaroni; cook 2 to 3 fewer minutes than manufacturers directions, until outside of pasta is cooked and inside is underdone. (Different brands of macaroni cook at different rates; be sure to read the instructions.)

6) Transfer the macaroni to a colander, rinse under cold running water, and drain well. Stir macaroni into the reserved cheese sauce.

7) Pour the mixture into the prepared casserole dish.

8) Sprinkle remaining 1 1/2 cups cheddar and 1/2 cup Gruyere; scatter breadcrumbs over the top.

9) Bake until browned on top, about 30 minutes.

10) Transfer dish to a wire rack to cool for 5 minutes; serve.