This salad borrows inspiration from the classic Waldorf, which combines fruits and nuts in a rich dressing. Our version is lighter and not as sweet as the original, thanks to the addition of a more calorie-conscious dressing and mildly bitter Belgian endive. It's easy to vary the recipe, substituting other fruits, nuts or greens as you choose.
Place the grapes, apple, pear, celery, and walnuts in a large bowl and toss to combine.
Cut the endives in half lengthwise and then slice crosswise in 1/2-inch wide strips. Add the endive to the bowl with the fruit.
Place the vinegar and sugar in a small bowl and stir to dissolve the sugar. Add the sour cream, buttermilk, lemon zest, and tarragon, and whisk to blend. Season generously with salt and pepper.
Add half the dressing to the bowl with the fruit mixture and toss to combine, adding more dressing as desired. Serve immediately if possible, or refrigerate for up to 2 hours.