Preheat oven to 375 degrees. Cook macaroni according to package directions.

Meanwhile, heat milk and butter in a medium saucepan over medium heat. Gradually whisk in flour, salt and dry mustard and simmer for 1 minute, whisking occasionally.

Remove from heat; stir in 2 cups of cheese until melted. Add drained macaroni to saucepan and toss with cheese sauce. Transfer mixture to an 8- or 9-inch square baking dish.

Bake uncovered in until hot and bubbly, about 20 minutes. Let stand 5 minutes before serving.

Variation
Make Mom add some color, and some extra nutrition. Sauté some chopped red pepper and broccoli florets in the butter before adding the flour for a gourmet version of this comforting creation.

Source: National Dairy Council