Baked mac and cheese using cheddar, mozzarella and American cheeses.
Cook macaroni according to directions in well-salted water. Drain. Set aside and cool to room temperature.
In small skillet melt butter. Add onion, salt and pepper. Sweat until water is mostly gone.
Put macaroni in large bowl. Add onions and butter mixture. Mix well until all the macaroni is covered with butter.
Add cheddar cheese and mix well.
Add mozzarella cheese and mix well.
Cover inside of deep 9x13 pan with cooking spray. Add 1/2 of the macaroni mixture and spread evenly.
Arrange American cheese slices evenly over this layer.
Add remaining macaroni mixture and spread evenly.
Pour milk evenly over the macaroni.
Place in oven and bake 45-60 minutes.