Cheesy Mashed Potato Pancakes

In a large bowl, stir together the mashed potatoes, cheese, scallions, egg and 3 tablespoons flour until combined. Using your hands, divide the mixture into 12 portions. Roll each portion into a compact ball then flatten it into a pancake about a 1/2-inch-thick. Place the remaining 1/2 cup of flour in a shallow dish and carefully dredge each pancake in the flour. Heat 3 to 4 tablespoons of vegetable oil in a large sauté pan over medium heat. Fry the pancakes, in batches, until they're golden brown and crispy on both sides, 3 to 4 minutes. Add more oil to the pan as needed between batches. Transfer the pancakes to a paper towel-lined plate and immediately sprinkle them with salt. Serve the potato pancakes topped with sour cream and garnished with additional chopped scallions.