The dressing for this salad is an adaptation of the classic Vitello Tonnato sauce that's usually served over thinly sliced veal tenderloin. It's a glorious combination of flavors that works equally well with fresh vegetables. You can substitute light versions of mayonnaise and sour cream without changing the flavor. Prep: 10 minutes.
1 small head romaine lettuce, torn into bite-size pieces
1 cup watercress, trimmed
1 cup sliced fresh fennel
1/2 medium cucumber, peeled, halved lengthwise, and sliced