You can also do the reverse.....Mashed potatoes leftover from yesterday's supper?
Put
cold mashed potatoes, some flour, chopped onions (I cook them to clear first), and some shredded cheese in a bowl, add enough water to be able to stir it up but remain sorta solid.
Of course it's a MK 1 eyeball type of thing as far as how much stuff you put with the mashed potatoes as it depends on the amount of leftover mashed potatoes.
Use a generous tablespoon full and place in a skillet, flatten it out some, cook till brown on both sides and you have the best potato cakes ever for breakfast. I usually just fry them in whatever breakfast meat grease I fixed. Bacon mostly.
Yes sir, no more warmed-over leftovers, left over to warm over.