In a mixing bowl, combine the cold leftover mashed potatoes, large egg, all-purpose flour, dry ranch seasoning mix, freshly shredded sharp cheddar cheese, salt, and black pepper. Mix everything together until well combined. The mixture should be thick enough to mold into patties.
With clean hands, take a handful of the mixture and shape it into a patty, about 1/2 inch thick. Repeat until all the mixture is shaped into cakes. You should be able to make around 6-8 cakes, depending on the size.
Place the 3 tablespoons of flour on a plate. Dredge each cake in the flour, ensuring that both sides are coated. This step will help create a lovely crispy crust when frying.
In a non-stick skillet, heat a couple of tablespoons of oil over medium heat. You want enough oil to coat the bottom of the skillet, but not so much that the cakes are swimming in it.
Once the oil is hot, carefully add the coated cakes to the skillet. Fry them for about 4-5 minutes on each side, or until they are golden brown and crispy. Avoid overcrowding the pan; you may need to do this in batches.
Once cooked, transfer the cakes to a plate lined with paper towels to drain excess oil. Serve warm, and enjoy the crispy, cheesy goodness!
