1. Remove the first layer of skin from your onion.
2. Peel your potatoes.
3. Grate the potatoes and onion using the large holes of a grater.
4. Melt the butter in a saucepan or in the microwave.
5. Add the flour, egg, melted butter, salt, pepper, and mix well. Heat a frying pan with oil. When it's hot, place small heaps of potato mixture and use a wooden spoon to shape them into pancakes that are not too thin or too thick.
6. Cook over medium heat for about ten minutes before flipping the pancakes like a crepe and continue cooking for another ten minutes on the other side. You can increase the heat towards the end of cooking to achieve a nice color.
7. When your rösti is golden brown on both sides, place it on paper towels to remove excess grease.
8. Remove the parsley leaves and chop them. Garnish your röstis with parsley.