We found that it’s crucial to cook the pasta until just past the al dente stage so that it doesn’t turn mushy as it sits in the sauce. Whole, low-fat, and skim milk all work well in this recipe. If desired, offer celery salt or hot sauce for sprinkling at the table.

6 slices hearty white sandwich bread, torn into quarters
5 tsp. unsalted butter, plus 3 T. cut into 6 pieces and chilled
1 pound elbow macaroni
Salt
6 tsp. all-purpose flour
1 ¼ tsp. dry mustard
1/4 tsp. cayenne pepper
5 C. milk
8 oz. Monterey Jack cheese, shredded (2 C.)
8 oz. sharp cheddar cheese, shredded (2 C.)

Pulse bread and 3 tsp. chilled butter in food processor to coarse crumbs, about 10 pulses; set aside. Adjust oven rack 8 inches from broiler element and heat broiler. Bring 4 quarts water to boil in large pot. Add macaroni and 1 tsp. salt and cook, stirring often, until tender; drain macaroni. Melt remaining 5 tsp. butter in now-empty pot over medium-high heat. Add flour, mustard, cayenne, if using, and 1 tsp. salt and cook, whisking constantly, until mixture becomes fragrant and deepens in color, about 1 minute. Gradually whisk in milk; bring mixture to boil, whisking constantly. Reduce heat to medium and simmer, whisking occasionally, until thickened, about 5 minutes. Off heat, slowly whisk in Monterey Jack and cheddar until completely melted. Add macaroni to sauce and cook over medium-low heat, stirring constantly, until mixture is steaming and heated through, about 6 minutes. Transfer mixture to 13 by 9-inch broiler-safe baking dish and sprinkle with bread-crumb mixture. Broil until topping is deep golden brown, 3 to 5 minutes. Let casserole cool for 5 minutes before serving.