Bring whole potatoes to a boil and boil until tender, about 15 minutes. (Boil eggs, drain and cool if using) Drain, halve and quarter potatoes. Place in a large bowl. In a small bowl, mix 1 tbs pickle juice and 1/2 tbs dijon mustard. Pour over potatoes, toss to coat. Refrigerate at least 30mins or up to 1 hour.