Cook potatoes in a large pot of boiling salted water over medium heat justuntil tender, 15-20 minutes. Meanwhile, make balsamic dressing: Whisk sourcream, Balsamic vinegar, olive oil, salt and pepper in a large bowl untilblended. Stir in all but 2 tb sliced scallions. Drain potatoes well in acolander. Transfer to bow; add dressing and gently toss to coat. Letpotatoes cool to room temperature. Add celery and radishes to potatoes inbowl and toss gently to combine. Line serving bowl with romaine leaves andspoon potato salad onto lettuce. Sprinkle salad with reserved scallions.
105 calories per serving.