Boil the potatoes: Peel the potatoes, cut them into large chunks, and boil in salted water until completely tender, about 15 to 20 minutes.
Drain and mash: Drain the potatoes very well through a colander, then mash until completely smooth and dry. Do not add milk, butter, or any moisture.
Season the mixture: Let cool slightly, then add the cornstarch, garlic powder, paprika, black pepper, salt, and parsley. Mix thoroughly until soft and pliable.
Portion the mixture: Take a portion about the size of a small clementine and flatten it in your palm into a small disc.
Fill with cheese: Place a cube of mozzarella in the center, then seal the potato mixture around it by gently folding and shaping into a cylinder or oval.
Optional chill: For extra stability, freeze the croquettes for 15 to 20 minutes before frying.
Heat the oil: Pour enough oil into a skillet to come at least halfway up the sides of the croquettes. Heat over medium heat until shimmering.
Fry the croquettes: Carefully place the croquettes in the hot oil and fry for 2 to 3 minutes per side, until evenly golden brown and crispy.
Drain and serve: Transfer the finished croquettes to a paper towel-lined plate to remove excess oil. Serve hot.
