Boil the potato cubes until soft. Drain them, mash while they’re still hot, and leave them aside to cool.
In a bowl, combine the mashed potatoes, cornstarch, salt, black pepper, and garlic powder. Mix until you have a firm dough. If it feels sticky, add a little more cornstarch.
Line a large tray with parchment paper and place the dough on it. Place another sheet of parchment paper on top and roll the dough out to about ¼ inch thick.
Peel off the top parchment paper and cut the dough into long strips with a knife or pizza cutter. Gently separate the strips as they can break easily.
Refrigerate the potato strips for about 45 minutes before frying.
Heat avocado oil in a deep fryer. Add the potato strips in batches to avoid overcrowding the pan. Fry for 4–5 minutes or until the fries turn golden brown.
Place the fries on a paper towel to soak up the extra oil. Sprinkle some grated Parmesan and chopped parsley on top.