This is a Martha Stewart recipe. She has a way of making recipes seem more elaborate than they really are; here I’ve condensed the instructions a bit. Please note – this is a double or triple batch! Which means you’ll spend about $427 on cheese alone, but, it’s worth it.
12 slices good-quality white bread torn into 1/4- to 1/2-inch pieces
2 sticks unsalted butter, plus more for dish
10 cups milk (2 1/2 quarts or 63% of a gallon, if you don’t want to measure)
1 cup all-purpose flour
4 teaspoons teaspoons kosher salt
1/2 teaspoon freshly grated nutmeg
1/2 teaspoon freshly ground black pepper
1/2 teaspoon cayenne pepper
9 cups (about 36 ounces) grated sharp white cheddar
4 cups (about 16 ounces) grated gruyere or 2 1/2 cups (about 10 ounces) grated pecorino romano
2 pounds elbow macaroni
Preheat the oven to 375 degrees. Butter a 3-quart casserole dish; set aside. Place bread pieces in a medium bowl. In a small saucepan over medium heat, melt 4 tablespoons butter. 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 12 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.
Remove the pan from the heat. Stir in salt, nutmeg, black pepper, cayenne pepper, 6 cups cheddar, and 3 cups Gruyere or 2 cups pecorino romano. Set cheese sauce aside.
Fill a large saucepan with water and bring to a boil. Add macaroni; cook 2 to 3 fewer minutes than manufacturer’s directions, until outside of pasta is cooked and inside is underdone. Transfer the macaroni to a colander, rinse under cold running water, and drain well. Stir macaroni into the reserved cheese sauce. Pour the mixture into the prepared casserole dishes. Sprinkle remaining 3 cups cheddar and 1 cup gruyere or 1/2 cup pecorino romano; scatter breadcrumbs over the top.
Freeze your extra dishes (or give them to friends with baking instructions). Bake until browned on top, about 30 minutes. Transfer dish to a wire rack to cool for 5 minutes then serve.