When you’ve got leftover mashed potatoes, the best way to revive them is to make them into mashed potato cakes. Add whatever herbs or flavorings sound good to you–hounds especially like chopped scallions and grated cheese. Some mix in an egg as a binder, but many find this is unnecessary, and can sometimes make the mixture too wet to shape easily. Drier mashed potatoes are easier to shape and pan fry, but potatoes rich in butter and cream can be dredged in seasoned flour and fried up well. Fry in olive oil or butter over medium heat until well browned on the bottom without moving, about 5-6 minutes, and flip to brown the other side. They’ll be crisp outside, soft and warm inside, and very satisfying.