Mashed potatoes (left over)
Cooked noodles
Sauteed onions in butter
Cheese

Spread mashed potatoes in an 8"x10" or 10"x12" pan. (One layer, put one layer noodles over mashed potatoes, one layer cheese, butter, sauteed onions.) Continue for 3 rows and add cheese on top. Bake at 350 degrees for 20 to 25 minutes or until cheese is melted.