1.Cook potatoes in boiling salted water for 10 to 12 minutes, or until just tender (do not overcook). Drain thoroughly.
2. Steam green beans in boiling water for 3 to 4 minutes, or until tender-crisp. Drain and immediately plunge into ice water to stop cooking process. Drain thoroughly.
3. In a large bowl, combine white wine vinegar, country Dijon mustard, salt and black pepper; slowly whisk in olive oil. Add red onion, capers and parsley; stir to blend. Add warm potatoes and green beans and gently toss to blend. Taste and adjust seasonings.
4. Serve at room temperature. If preparing ahead, remove from refrigerator 10 minutes before serving and then gently toss to blend.
Optional: This French potato salad is delicious paired with a warm crusty baguette layered with brie cheese, French ham and fresh spring greens for a Paris picnic basket.