Ingredients for 6 servings:
1. 3/4 lb green beans
2. 3 lbs cooked small boiling potatoes, cooled and quartered
3. 1 cup mayonnaise
4. 3 tablespoons tarragon vinegar or 3 tablespoons white wine vinegar
5. 3 scallions, chopped
6. 3 flat anchovy fillets, chopped or 2 teaspoons anchovy paste
7. 1/4 cup chopped fresh flat-leaf parsley
8. 2 teaspoons chopped fresh tarragon
9. 1 teaspoon salt
10. 1/2 teaspoon black pepper

Directions:
1. Cook beans in a 3-quart saucepan of boiling salted water, uncovered, until tender crisp, 3-5 minutes.
2. Drain in a sieve, then plunge the sieve into a large bowl of ice water to stop the cooking.
3. Drain again, pat beans dry and then cut into 1/4 inch pieces and put in a large bowl with the potatoes.
4. Pulse mayonnaise, vinegar, scallions, anchovies, parsley, tarragon, salt and pepper in a food processor, or blender, until dressing is pale green and herbs are finely chopped.
5. Stir into potato mixture.