Step 1In a food processor or blender, puree the anchovies, green onions, parsley, tarragon, vinegar and chives, or grind with a mortar and pestle to make a fairly smooth paste. Stir the mixture into the mayonnaise. Refrigerate tightly covered. This will make just over 1 1/2 cups dressing, more than enough for the salad.
Step 1Pull away any tough or faded outer leaves from the romaine, then separate the heads into individual leaves and combine in a mixing bowl.
Step 2Place the shrimp in another small mixing bowl with the watercress leaves and add just enough Green Goddess dressing to lightly coat, about 2 tablespoons.
Step 3Spoon about one-half cup of the remaining Green Goddess dressing over the romaine and toss, adding more dressing 1 tablespoon at a time as needed to lightly coat the leaves.
Step 4Arrange the romaine on 6 chilled salad plates, then arrange the shrimp and watercress on top and serve immediately.