Peel the russet potatoes and rinse them under cold water to remove surface dirt. Use a box grater or food processor to shred them into thin, even strands. Russet potatoes work particularly well because their high starch content helps create a crisp exterior.
Place the shredded potatoes in a bowl of cold water and stir briefly. Drain through a colander, then rinse once more if the water looks very cloudy. This step helps remove excess surface starch, which can make the potatoes stick together.
Transfer the shredded potatoes to a clean kitchen towel or cheesecloth. Gather the edges and squeeze firmly over the sink to remove as much water as possible. For crisp hash browns, the potatoes should feel relatively dry before cooking.
Place the dried potatoes in a large bowl. Add the salt, black pepper, and optional garlic powder and chopped onion. Toss gently until the seasonings are distributed evenly. If using onion, squeeze out any excess liquid before adding it to the potatoes.
Place a large nonstick or cast-iron skillet over medium-high heat. Add about 2 tablespoons of vegetable oil and allow it to heat until shimmering but not smoking. A properly heated pan helps the potatoes develop a golden crust instead of absorbing too much oil.
Spread the shredded potatoes in an even layer in the hot skillet, forming four smaller portions or one large patty. Press gently with a spatula to help the strands make contact with the pan. Cook undisturbed for about 5–7 minutes, until the underside is deep golden brown and crisp.
Drizzle the remaining oil around the edges of the potatoes if needed. Flip the hash browns carefully with a wide spatula, working in sections if necessary. Cook for another 5–7 minutes, until the second side is golden and the potatoes are tender throughout. Reduce the heat slightly if they brown too quickly.
Transfer the cooked hash browns to a plate lined with paper towels or a wire rack to remove excess oil. Taste and add a little more salt if needed. Serve immediately while the edges are crisp and the centers are hot.