01 - In a large mixing bowl, add mashed potatoes, cheddar cheese, mozzarella cheese, egg, flour, salt, and black pepper. Mix thoroughly until all ingredients are well combined.
02 - Using clean hands or a scoop, form the mixture into evenly sized balls, each approximately the size of a golf ball.
03 - Roll each ball gently in bread crumbs, ensuring they are evenly coated on all sides.
04 - Pour oil into a large frying pan to a depth of 1 inch and heat over medium heat until shimmering.
05 - Working in batches, gently lower the cheese puffs into the hot oil and fry for 4 to 5 minutes per batch, turning occasionally, until all sides are golden brown.
06 - Transfer fried puffs onto a plate lined with paper towels to drain any excess oil.
07 - Arrange the cheese puffs on a serving platter and serve immediately while hot.