Wash potatoes and place in a saucepan. Cover with water and cook until tender, about 30 minutes. Drain and let cool to touch. Peel potatoes and cut into slices. There should be about 6 cups.
Heat oil and 2 tablespoons butter in a large skillet over medium heat. Add potatoes and season with salt and pepper to taste. Cook potatoes, while tossing and shaking pan, about 10 minutes until golden and crusty on both sides. Add remaining tablespoon of butter. Add garlic and parsley.