Place potatoes in large saucepan; add enough water to cover potatoes. Bring to boil. Cook on medium heat 10 to 15 minutes, just until potatoes are tender. Drain well; allow to cool slightly.
Meanwhile, mix Mustard, vinegar, oil, salt and pepper in large bowl with wire whisk. Add potatoes and parsley. Toss gently until well mixed. Serve immediately or refrigerate until ready to serve.