1Preheat oven to 375*
In a Medium sauce-pan, melt butter; stir in flour, mustard, and salt. Gradually stir in milk. Cook & stir until mixture thickens slightly. ( Mixture should coat spoon) Remove from heat. Add 4 cups cheese; Stir until melted. Stir in cooked macaroni into the sauce mixture.
2Grease large casserole dish. Pour Macaroni into the dish and top with 2 cups (or less) of grated cheese. Last but not least, sprinkle the cooked bacon bits all over top of macaroni casserole. Bake for 20-25 minutes or until casserole is bubbly and a tad browned ontop. OH BABY! :) ENJOY!