In a large mixing bowl, combine mashed potatoes, cheese, egg, flour, salt, and pepper. Mix until a cohesive dough forms, about 3-5 minutes.

With slightly wet hands, take small portions of the mixture and roll them into bite-sized balls, approximately 1-2 inches in diameter.

In a deep pan, pour enough cooking oil to cover the bottom by about 1-2 inches. Heat the oil over medium heat until it's 350°F (175°C).

Once the oil is hot, gently place the potato puffs in the oil. Fry them in batches for about 3-4 minutes until golden brown.

Remove the puffs using a slotted spoon and transfer them to a paper towel-lined plate to drain. Serve warm.