Peel and grate 450 g potatoes, then mix with 1 t salt and 1⁄4 t freshly ground black pepper. Allow to rest for 5 minutes. Using your hands, squeeze out as much liquid from the grated potato as possible and place it in another bowl.
Heat 2 T butter and 1 T canola oil in a 23-cm cast-iron pan. Add handfuls of potato to the hot pan and spread it out in an even layer. Reduce the heat and cook until the bottom has browned and the top is slightly translucent.
The trick to flipping the rösti: Cover the pan with an upturned plate, invert the pan, then slide the rösti back into the pan to cook the other side.
Each side should take approximately 7 minutes. Slide the rösti from the pan onto a plate and cut into 4 wedges. Serve with sour cream and salmon roe, or a poached egg and blanched spinach.