Heat a skillet over medium heat and add the canola oil. Add the onions, season with a pinch of salt and cook, stirring frequently, until the onions are golden brown, 15 to 20 minutes.
Meanwhile, season the potatoes with salt and pepper and let sit for 5 minutes. Drain out the excess moisture.
Set individual cast-iron pans over medium heat until very hot. Add some olive oil to each pan and a handful of the potatoes. Cook until golden brown and crispy, about 5 minutes. Flip and add more oil if necessary. Cook until golden brown on the second side and cooked through. Repeat with the remaining potatoes.
Top each hash brown with some caramelized onions and a dollop of sour cream and chopped scallions.
For a nice alternative, serve them topped with caviar, sour cream and chives. You can also make smaller ones, similar to latkes, if desired. In that case, I would add an egg and a little flour to the potato mixture.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.