1)Cook macaroni according to package directions. Drain and set aside.
2)Preheat oven to 375 degrees.
3)In saucepan over medium heat, melt butter. Then add flour, salt, dry mustard, pepper and stir until smooth.
4)Gradually stir in milk. Stir constantly until thickened or approximately 10 minutes.
5)Remove from heat. Stir in 1 1/2 cup cheese until melted.
6)Pour in cooked macaroni and stir until well combined.
7)Spray 2 quart casserole dish with non-stick cooking spray.
8)Pour mixture into prepared dish. Sprinkle 1/2 cup cheese on top and bake for approximately 25 minutes or until lightly browned.
9)Serve this warm and gooey dish cut into individual portions and enjoy!