Cook macaroni as directed on the package until al dente. Drain and set aside.
Preheat oven to 400 degrees
Melt butter in a sauce pan. Add flour, salt, pepper, cayenne pepper, and ground mustard. Whisk together until well-blended and without lumps and then add in minded garlic. Cook flour mixture over medium heat for 3 minutes
Pour in milk while whisking. Bring to a simmer and let simmer for 2 minutes, stirring frequently.
Reduce heat to low-medium and cook for 10 minutes, stirring frequently
Stir in 1 cup of sharp cheddar and 1 cup of mild cheddar (setting aside 1/4 cup of mild cheddar for the top). Cook until cheese is melted.
Stir macaroni into cheese sauce and then transfer macaroni into a baking dish that has been greased with cooking spray.
Top with the reserved 1/4 cup of mild cheddar cheese. Sprinkle with bread crumbs and garlic salt.
Bake for 20 minutes until bubbly and golden brown.