Thaw the frozen shredded potatoes. (Alternatively, shred your own potatoes using a coarse grater. Rinse the shredded potatoes and dump them onto a kitchen towel. Squeeze to remove the excess moisture.)
Add the potatoes to a large bowl. Add melted butter, onion and garlic powders, and salt and pepper. Toss to incorporate the seasonings.
Preheat a large non-stick skillet over medium heat with a generous drizzle of oil. A cast-iron skillet works well too! Add the potatoes to the skillet and with the back of a spatula, press the potatoes firmly into an even layer. Cook for 15-20 minutes until golden brown and crispy on the bottom.
To flip the hash browns, place a large plate upside down on top of the skillet. Flip the skillet over, inverting the hash browns onto the plate. Add more oil to the skillet and slide the hash browns back into the skillet. Cook for another 10 minutes until the bottom is golden and crispy.
Slide the hash browns onto a board or serving platter. Garnish with scallions and a touch of salt. Slice and serve with sour cream. I love serving with horseradish sour cream. Just add prepared horseradish - as much as you like - to sour cream and stir.