01 - In a large mixing bowl, thoroughly combine cold mashed potatoes with cheddar cheese, green onions, garlic powder, black pepper, salt, and one egg until the mixture is uniform.
02 - Portion heaping tablespoons of the mixture and roll between your palms to form balls approximately 1 1/4 inches in diameter. Arrange on a tray.
03 - Place flour in one bowl, beaten eggs in a second bowl, and breadcrumbs in a third bowl for breading the potato balls.
04 - Dredge each potato ball in flour, dip in beaten eggs, then roll in breadcrumbs to coat evenly.
05 - Place breaded balls on a tray and refrigerate for at least 20 minutes to firm and set the coating.
06 - Pour vegetable oil into a deep fryer or heavy-bottomed pot and bring to 350°F.
07 - Working in batches, carefully lower chilled potato balls into hot oil and fry, turning occasionally, for 2 to 3 minutes until golden brown and crispy.
08 - Use a slotted spoon to transfer fried potato balls onto paper towels to drain excess oil. Serve immediately while hot.