Meanwhile, in a small bowl, whisk together the wine, chicken stock, lemon juice, garlic, mustard, 2 teaspoons salt and 3/4 teaspoon pepper. Slowly whisk in the olive oil to make an emulsion. Set aside.
When the potatoes are cool enough to handle, cut them into quarters or halves, depending on their size. Place the cut potatoes in a large bowl and pour enough dressing over them to moisten. (As the salad sits, you may need to add more dressing.) Add the onion, tarragon and parsley, and salt and pepper to taste. Toss well, cover, and refrigerate for a few hours to allow the flavors to blend. Serve cold or at room temperature.