Prepare the Potato Mixture: In a bowl, mix mashed potatoes, Parmesan cheese, egg yolk, melted butter, salt, black pepper, garlic powder, and parsley until well combined. Shape into small cylinders or balls and refrigerate for 15-20 minutes to firm up.
Coat the Croquettes: Roll each croquette in flour, then dip in beaten egg, and finally coat with breadcrumbs, ensuring an even layer.
Fry to Perfection: Heat oil in a pan over medium heat. Fry the croquettes in batches for 2-3 minutes per side, until golden brown and crispy.
Drain & Serve: Transfer to a paper towel-lined plate to remove excess oil. Serve warm with garlic aioli, ketchup, or your favorite dipping sauce.