using a ratio of
1 cup of leftover mashed potatoes: 1 egg (2 cups patatoes to 2 eggs, etc)
combine and mix well. You can add salt and pepper, shredded cheese, green onion, shredded carrots, whatever to these.
Shape into patties and fry in a skillet. Spray oil is okay to use but regular oil will fry them up much nicer and they will hold together and not stick to the pan