1) In a large saucepan, add potatoes to enough water to cover. Bring to the boil, and cook for 8 minutes. Add French beans, return to the boil and cook for 2 minutes. Drain and cool slightly.
2) Place potatoes and French beans in a serving bowl.
3) In a small bowl, whisk together olive oil and white wine vinegar, mustard, dill, salt and pepper. Pour over potato and French beans, tossing gently to coat. Cover and chill.