Use a large pot, pop in the potatoes and cover with water. Place on stove and bring to a boil. Cook for about 20 to 25 minutes, they should be fork tender.
Remove and drain potatoes.
Allow to dry for about 5 to 8 minutes.
Take your palm and gently press down on the potatoes to break the skin and flatten them a bit.
Place a cast iron skillet over medium heat, add olive oil and onions. Cook the onions for about 5 to 7 minutes, until the start to soften. You can remove the onions and set aside.
Now place the potatoes in the pan, you'll likely do about 2 or 3 batches depending on the size of your skillet. Cook for about 5 to 8 minutes on each side. They should start to turn brown and soften up some more.
Once you get all the batches down, pop them all back in the skillet with the onions and cook over medium low heat for about 2 minutes to just warm everything back up.
Remove and place in a bowl.
Sprinkle with parsley.