Mix mashed potatoes, flour, onion, egg, black pepper, and salt in a bowl until well combined, similar to a batter consistency.
Heat vegetable oil in a skillet over medium heat. Drop 4-inch circles of batter into the hot oil. Cook until golden brown, about 4 to 5 minutes per side; drain on paper towels. Repeat with any remaining batter
We have determined the nutritional value of oil for frying based on a retention value of 10% after cooking. The exact amount will vary depending on cooking time and temperature, ingredient density, and the specific type of oil used.