01 - Using the large holes of a box grater, grate the potatoes and, if using, the onion.
02 - Place grated potatoes and onion in a clean kitchen towel and squeeze out as much moisture as possible.
03 - Transfer the grated mixture to a large bowl and toss evenly with salt and black pepper.
04 - Heat 1 tablespoon butter and 1 tablespoon vegetable oil in a large nonstick or cast-iron skillet over medium-high heat.
05 - Spread half of the potato mixture evenly in the pan about 1/2 inch thick and press down lightly with a spatula. Cook undisturbed for 4 to 5 minutes until the bottom is golden brown and crisp.
06 - Carefully flip the hash browns using a wide spatula, add another tablespoon of butter if necessary, and cook for an additional 4 to 5 minutes until crisp and golden on the opposite side.
07 - Transfer cooked hash browns to a plate lined with paper towels. Repeat cooking process with the remaining potato mixture and fats.
08 - Serve hot, optionally garnished with chopped chives or your preferred toppings.