Step 1

Make the macaroni and cheese: Bring a large pot or Dutch oven of heavily salted water to a boil over high heat. Add the pasta and cook until al dente. Drain, rinse with cold water until cool to the touch, and set aside to drain thoroughly.

Step 2

In the now-empty pot, heat 4 tablespoons of the butter over medium-high heat until foaming. Add the flour, salt, mustard, and cayenne if using and whisk well to combine. Continue whisking until the mixture becomes fragrant and deepens in color, about 1 minute. Gradually whisk in the milk and bring to a simmer, whisking frequently.

Step 3

Reduce the heat to medium and simmer, whisking frequently, until thickened slightly, about 2 minutes. Remove from the heat. Add both cheeses and whisk until smooth and fully melted. Set aside until cooled to just warm to the touch, about 30 minutes.

Step 4

Meanwhile, melt the remaining 1 tablespoon of butter and place in a medium bowl. Add the cracker crumbs and stir to combine; set aside.

Step 5

When the sauce is cooled, add the pasta and stir to combine. Transfer to a 9x13-inch baking dish and spread into an even layer. Sprinkle the cracker crumbs evenly over the macaroni and cheese. Cover tightly with aluminum foil and refrigerate for up to 2 days.

Step 6

When ready to bake: Arrange a rack in the middle of the oven and heat to 400°F. While the oven is heating, let the baking dish sit out at room temperature.

Step 7

Bake covered until heated through and bubbling around the edges, about 45 minutes. Uncover and bake until the top is golden-brown, about 15 minutes more. Let sit 5 minutes before serving.