Directions

1. Adjust oven rack to middle position and heat oven to 350 degrees.
2. Pulse bread, melted butter, and Parmesan cheese in food processor until ground to coarse crumbs, about 8 pulses. transfer to a small bowl.
3. Bring 4 quarts of water to a boil in a large pot. Add macaroni and 1 tablespoon of sale and cook, stirring often, until just al dente, about 6 minutes. Reserve 1/2 cup macaroni cooking water, then drain and rinse macaroni in colander under cold running water. Set aside.
4. Melt remaining 4 tablespoons of butter in now empty pot over medium-high heat. Stir in flour and cook, stirring constantly, until mixture turns light brown, about 1 minute. Slowly whisk in evaporated milk, hot sauce, mustard, nutmeg, and 2 teaspoons salt and cook until mixture begins to simmer and is slightly thickened, about 4 minutes. Off heat, whisk in cheeses and reserved cooking water until cheese melts. Stir in macaroni until completely coated.
5. Transfer mixture to 13 x 9-inch baking dish and top evenly with bread-crumb mixture Bake until cheese is bubbling around edges and top is golden brown, 20 - 25 minutes. Let sit for 5 to 10 minutes before serving.