Generously butter a 9x13 pan. Spread 2 cups of mashed potatoes on the bottom pan. Sprinkle with 1 cup of cheese. Place 3 noodles over the layer of cheese. Repear layers. For the final layer, spread the remaining potatoes over the last layer of noodles. Sprinkle with the remaining cheese (use anywhere from 1-2 cups on this final layer), bacon (if using) and then cover with foil.
Bake for 40 minutes and then remove foil. Bake for another 20 minutes, until cheese is browned.
Allow to cool before slicing.
Serve as is, or with caramelized onions and a dollop of Greek yogurt or sour cream.
Use any of your family's favorite mashed potato recipe for this leftover potato casserole
This recipe does not work with the "oven-ready" lasagna noodles, to the lack of excess moisture in the mashed potatoes.
Leftovers can be store in an airtight container for up to 4 days in the refrigerator. This lasagna does not freeze well.