Classic baked macaroni and cheese is a comfort food favorite that is loved by people of all ages. It is creamy, cheesy, and gooey, and it is perfect for any gathering. It is a very versatile dish that can be easily made ahead of time and reheated.
In a large saucepan or saucier over medium-low heat, melt the butter.
When the butter begins to sizzle slightly, add the flour, dry mustard, and salt. Whisk with the butter to form a light roux.
Whisk in the milk one cup at a time; continue whisking until the sauce has thickened slightly.
Reduce heat to low. Whisk in 12 ounces of shredded cheddar cheese, one handful at a time, until melted after each addition. Stir until smooth without letting the sauce boil vigorously. Keep warm over low heat, stirring occasionally to prevent burning. Reserve the remaining 4 ounces of cheese for the topping.
Cook the pasta according to package directions for al dente. Drain without rinsing, then return it to the pot.
Pour the hot cheese sauce over the pasta and stir to combine.
Coat a 9 × 13-inch baking dish with nonstick cooking spray.
Transfer the macaroni and cheese to the prepared dish and top with the reserved 4 ounces of shredded cheddar.
Bake in the preheated 375°F oven for 30 minutes, until golden and bubbly.
Remove from the oven and let stand for 5 to 10 minutes before serving.