Melt the butter in a small saucepan over medium heat until it turns liquid and starts to bubble slightly. Add the minced garlic and stir constantly so it doesn't burn or turn bitter. Cook for just one to two minutes until fragrant, then set it aside to cool.
Place the potato chunks in a large pot and cover them with cold water. Bring the pot to a boil over medium-high heat and let the potatoes cook for eight to nine minutes. They should still have some resistance when poked with a skewer, not fully soft.
Drain the parboiled potatoes right away and spread them out on a baking sheet. Let them sit for six to eight minutes until they're cool enough to handle comfortably. Skipping this cooling step can make grating messy and difficult.
Grate the cooled potatoes directly into a large mixing bowl using a box grater. Add the cooked garlic, parmesan, egg, cornstarch, salt, white pepper, and onion powder if using. Stir everything together until it's evenly combined and holds together well.
Line a baking sheet with parchment paper and divide the mixture into eight equal portions. With slightly wet hands, shape each portion into a patty or your preferred hash brown shape. Wetting your hands again between portions keeps the mixture from sticking.
Cover the shaped hash browns with plastic wrap and place the tray in the freezer. Let them firm up for 45 to 60 minutes so they hold their shape during frying. This step makes a big difference in how crispy and intact they turn out.
Heat about two cups of oil in a large skillet to 350°F. Fry the chilled hash browns in batches for six to eight minutes, flipping halfway, until deeply golden and crisp. Transfer them to a wire rack over paper towels to drain excess oil.
Grate a little extra fresh parmesan over the hot hash browns right before serving. Serve them immediately while they're still warm and at their crispiest. This final touch makes them look and taste even more irresistible.