In a large bowl, combine cold mashed potatoes, scallions, cheese and egg.
Add 3 tablespoons of flour. If mixture needs additional flour, add up to 3 more, one tablespoonful at a time until potatoes come together.
Form potato mixture into pancakes about 1/4 inch thick.
Place remaining 1/2 cup of flour on a plate and dredge both sides of the pancakes in the flour.
Meanwhile, heat vegetable oil over medium high heat.
Carefully add pancakes and fry in batches until gold brown on both sides, about 3-4 minutes on each side.
Add additional oil if needed between batches.
Season with salt and pepper as soon as they are removed from the frying pan.
Serve with sour cream.
Notes
Seasonings: Enhance the flavor of your potato cakes with a sprinkle of your favorite seasonings. All-purpose seasoning or a touch of garlic powder can add an extra layer of deliciousness. Or you'll love adding a little grated onion to the creamy mash potato mixture.
Toppings: Don't forget to top your potato cakes with your favorite garnishes like sour cream, chives, or a dollop of zesty salsa.
Store Bought Mashed Potatoes: Use up leftover mashed potatoes is ideal, store-bought varieties can also be used for an easier side dish.
Cauliflower: Make a low carb version of this cake by using mashed cauliflower. Cook, grate and mash your own or use store bought.