6 c. mashed potatoes (can be leftover or instant)
1 lb. Cheddar cheese, grated
2 sticks butter, melted
1 lg. onion, diced
1 lb. lasagna noodles, cooked

Saute onion in butter until wilted. Butter 13x9x2 dish.

Place a layer of noodles, then potatoes, then cheese, then 1/3 of onion/butter mixture. Repeat layers ending with noodles. Pour remaining onion/butter mixture on top. Cover with foil and bake at 350 degrees for 30 minutes.