In a small saucepan under medium heat, melt the butter. Add in the garlic and cook while stirring just until the garlic starts to softened and become fragrant, about 1-2 minutes. Remove from heat and set aside.
Add the potatoes into a large pot filled with cold water and bring to a boil over medium high heat. Parboil the potatoes for 8-9 minutes. If you were to poke one of the potato chucks with a skewer, it should not go all the way through and you should have some resistance.
Drain parboiled potatoes. Transfer to a baking sheet and spread out to cool, about 6-8 minutes, or until cool enough to handle.
In a large mixing bowl, grate the cooled potatoes with a box grater. Add in the cooked garlic, parmesan cheese, egg, cornstarch, salt, white pepper, and onion powder (optional). Give mixture a good mix to combine.
Line a large baking sheet with parchment paper. Divide the hashbrown mixture into (8) equal portions. With lightly wet hands, shape each portion into desired hashbrown shape and transfer to prepared baking sheet (Re-wet hands as needed in between shaping the hashbrowns).
Cover baking sheet with plastic wrap and place in the freezer for 45-60 minutes.
Heat oil (about 2 cups) in a large pan or skillet to 350F. In batches, fry the chilled hashbrowns until crispy and richly golden brown, about 6-8 minutes (3-4 minutes per side) or longer as needed. Transfer to a wire rack placed over a paper towel lined baking sheet to catch any excess oil.
Finely grate fresh parmesan cheese over the hashbrowns before serving (optional). Serve immediately while still crispy and warm with your favorite dip or sauce. Enjoy!