Put the potatoes in a large saucepan and cover with water. Bring to the boil and simmer for 12-15 minutes, or until tender. Drain, rinse with cold water and then leave to cool.
Whisk together the olive oil, vinegar and Dijon mustard. Season with black pepper. Drizzle the dressing over the potatoes and stir well to ensure the potatoes are well coated. Add the shallots, diced gherkins and parsley. Stir well and serve.