Traditionally, potato pancakes are made using grated potatoes as the main ingredient. After finely grating the potatoes, you drain off excess liquid and then mix the spuds with an egg and flour, which bind everything together. Finally, you fry them in a pan. Many other ingredients, such as onions and spices, can make an appearance, too, but that's the general idea.
Leftover mashed potatoes make a great substitute for the grated potatoes in this dish, simply because they're all ready to go -- no peeling, grating or blotting up excess liquid. It can also be a tad easier to mix in additional ingredients, since the potatoes are mashed and not in small slices. And you're only limited by your imagination when it comes to what you can add to your mashed potato pancakes. Try some ginger, cinnamon, maple syrup and leeks for a sweet-and-savory taste. Or select your favorite herbs, plus some cheese, to create a breakfast-friendly alternative to home fries or hash browns.