Using a large grater or food processor, shred the potatoes. Transfer shredded potatoes into a large bowl and fill with cold water until potatoes are covered. Let potatoes rest for 5 minutes, then transfer into a colander and press out as much liquid as possible.
Place shredded potatoes on a clean kitchen cloth or paper towels and continue pressing until very dry. (Tip: The secret to making golden brown hash browns at home is to press as much liquid as possible out of the shredded potatoes!)
Meanwhile, add vegetable oil to a cast iron skillet and place over medium-high heat until hot. Add butter and swirl the pan until the oil and butter have evenly coated the bottom of the skillet. Add the shredded potatoes and cook over medium-high heat for 10-12 minutes. (Tip: Don’t stir or flip the potatoes at this stage unless they are beginning to burn.)
Flip the hash browns, reduce heat to medium and continue cooking for another 7-8 minutes, or until potatoes are golden brown in color.