Heat oven to 375 degrees. Spray 10-inch pie plate or casserole dish with cooking spray. Place uncooked macaroni in pie plate. Mix shredded cheeses. Spread 2 1/2 cups cheese on top of macaroni.
In medium bowl, stir remaining ingredients (except remaining 1/2 cup cheese) with wire whisk or fork until blended. Pour into pie plate on top of macaroni.
Spray sheet of foil with cooking spray; place sprayed side down over pie plate. Bake 40 minutes. Uncover; bake 8 to 10 minutes longer or until knife inserted in center comes out clean. Sprinkle with remaining 1/2 cup cheese. Bake 2 to 4 minutes longer or until cheese is melted. Let stand 5 minutes before serving.