The Fried Egg is an item that first appeared in Paper Mario. Tayce T. could cook one for Mario by simply frying an egg. A Fried Egg replenishes 10 HP and sells for 7 Coins.
In Paper Mario: The Thousand-Year Door, Zess T. could make a Fried Egg by frying a Mystic Egg, instead of a normal Egg. It also healed 10 HP. Also, in the first chapter when you play as Bowser, Kammy Koopa asks if he liked Fried Eggs. Whichever option the player choses has no impact on the story.
In Super Paper Mario, Fried Eggs can be made by Saffron by cooking a Big Egg. The item restores 15 HP and cures poison.