My favorite leftover treatment is yet another family solution I grew up with: the fried mashed potato cake, which I have given a much fancier name in order to entice you with its fanciness. Of course, the fact that these are delicious is so obvious as to be almost tautological. What if you added grated cheese to something, then breaded it and fried it in butter and it was anything short of lip-smacking? That would be a more or less existential kind of crisis, for which there would be no solution. Oh, but these are crazy-good: the mashed potatoes go all molten inside their buttery-crisp Corn-Chex-crumb shell (breadcrumbs are perfectly fine too), and then they're laced with cheddar and just the tiniest tingling bite from the pickled jalapenos. Of course, you could swap in any other kind of cheese for the cheddar and omit the peppers if you like, and yes, of course, they will still be golden disks of spudly heaven--and also, then you can serve them with sour cream and applesauce and pretend you made them on purpose for Chanukkah.
Yields 8 fritters
In a bowl, stir together the mashed potatoes (heat them first in the microwave if they're cold), the cheese, and the jalapenos.
Put the cereal in a Ziploc bag and finely crush it with a rolling pin, then dump it onto a plate.
Now use a cookie scoop or a tablespoon to lift out giant, heaping tablespoons of the potato mixture, which you will roll into balls and then flatten into patties. Press the patties into the crumbs, coating each side well.
Heat the butter and oil over medium heat in a large, nonstick frying pan until a crumb sizzles if you drop it in. Fry the potato cakes, about three or 4 minutes per side, until they are deeply golden, flipping them very gently in the middle of cooking. Serve them piping hot with sour cream and salsa (we didn't have any salsa, actually, and didn't miss it).