A pierogi casserole recipe with lasagna noodles, mashed potatoes, American cheese, butter, and onions.
Spray a 9 x 13 baking dish with nonstick spray.
Lay 3 - 4 lasagna noodles in one layer, overlapping slightly as needed, in the bottom of the baking dish.
Spread 2 cups of mashed potatoes evenly over the noodles.
Sprinkle 1 tablespoon of minced onion over the mashed potatoes.
Layer 6 slices of American cheese and 5 thin slices of butter.
Repeat these layers twice more, for a total of three layers.
Cover with foil and bake at 350 degrees for 25 - 30 minutes or until cheese is melted.
Store leftovers tightly covered in the refrigerator.