These Mashed Potato Cakes are my favorite way to breathe new life into leftovers. Instead of just reheating a bowl of potatoes, you’re turning them into something with a salty, golden-brown crust and a center that stays incredibly fluffy. It’s a simple, three-ingredient trick that takes about 20 minutes from start to finish.
Mix the egg into the mashed potatoes with a fork until well blended. Add the flour and onions (if using onions) and mix well. The mixture will be very stiff.
Pour approximately 2 tablespoons of oil into a cast-iron skillet and heat over medium heat.
Scoop out heaping tablespoons of mixture into the hot oil. Dip the back of a spoon into the oil and then the mashed potato mixture to flatten to about a 1/4-inch thick. By dipping the back of the spoon into the oil, the spoon will not stick to the potatoes, making flattening them much easier.
Fry until golden brown and then flip and continue to brown the potato patty on the other side.