Sprinkle the crumbs: In a 10-inch ovenproof skillet (I use this one), melt two tablespoons of butter over medium heat and add the breadcrumbs. Dip the crumbs in the butter, stir, until golden brown. Season with a little salt and scrape the crumbs into a bowl to set aside. Swipe the pan to clean it, if you like. No one will notice if the crumb ends up in the sauce, though.
Toss your pasta: Place the uncooked pasta in a large bowl and cover with hot water. Knead for 10 minutes and take it out, shaking the pasta. (I find it holds a lot of water.)
Make the sauce and combine: Combine the three cheeses right on the paper or board you wrapped them in.
Return your ovenproof skillet to the stove over medium heat and melt the remaining 3 tablespoons of butter in it. Add the flour, stirring to combine. Add the milk, 1/2 cup at a time, whisking to combine each addition with the butter-flour mixture until smooth. When all the milk has been added, season with 1 1/2 tablespoons of kosher salt (diamond brand; use half of any other brand), several grinds of black pepper, cayenne, and nutmeg, and cook, stirring, until the mixture comes to a boil again. it starts to thicken. Once boiling, cook for 2-3 minutes, stirring. Turn off the burner.
Setting aside 2/3 cup of the cheese mixture, add the rest of the cheeses to the sauce, and stir until melted. Taste the sauce (carefully!) here and adjust the seasoning if needed to taste. Stir in the minced pasta until evenly combined. Sprinkle the top with the reserved cheese, followed by the toasted breadcrumbs.
Bake: Transfer the skillet to the oven and bake, uncovered, for 30 minutes. You can fish a piece of macaroni to make sure it’s cooked, but I’ve never found this to be a problem. Add another 5 minutes in the oven, if needed to soften. If you want it to brown a little more, run the pan briefly under your broiler for a minute.
Serve: Let rest for 2 to 3 minutes, then serve immediately.
Do it ahead: Given the choice between reheating cooked macaroni and cheese and baking it fresh, and since it takes about the same amount of time in the oven to bake it as to reheat it, I always choose to bake the mac and cheese before serving. You can put it together ahead of time, though, and bake before you’re ready to eat. Reheat leftovers in original pan or ovenproof dish at 350°F for 20 to 30 minutes.
