To begin, wash your potatoes. I used a variety of gold, red, and purple potatoes. Place the whole potatoes in your pot and cover with water. Sprinkle in a good pinch of salt and bring them to a boil. Reduce the heat to medium and simmer for about 20 minutes or until you can stick a fork in a potato with little resistance.
Meanwhile, finely dice your onion. Place the diced onion in a saucepan along with the red wine vinegar, olive oil, chicken broth, and Dusseldorf style mustard. If you can’t find this, then simply use any strong yellow mustard. Add in the salt & pepper. Bring this to a boil, reduce the heat, and let it cook just until the onions are tender, stirring occasionally. Remove from heat.
Once the potatoes are done cooking, drain them and let them cool enough so that you can handle them. Slice your potatoes into half inch slices. If you want, you can peel them first. Once your potatoes are all sliced, place them in a serving or mixing bowl.
Squeeze the lemon juice into your liquid in the sauce pan and pour this all over the potatoes. Finally sprinkle in the parsley. Gently stir this all together and then let it cool to room temperature.