Beat egg in a medium size mixing bowl. Mix egg and onion with mashed potatoes. Add salt and pepper.
Heat olive oil in a medium size frying pan, over a medium heat. Scoop the potato mixutre into the frying pan in 4 inch circles, pat with a spatula to flatten the mounds to approximately 1/2 to 1 inch thick. Cook until bottom is browned. Flip the patty over and brown on the other side.
