Grate onions and potatoes.
Toss together with salt and pepper.
Add potato mixture to a preheated pan prepared with cooking spray.
Using a spatula, press into the pan, smoothing and tucking in the edges.
Allow to cook for about 5 minutes or until golden.
Using a small plate places over the skillet, flip and then slide back into the skillet. Cook for another 5 minutes.
If your skillet is oven-safe, you could finish the cooking in the oven to cook through and get a crispier exterior.
Cut into wedges and erve with vegan sour cream and a sprig of parsley.