6 medium celery ribs, peeled and thinly sliced crosswise on a mandoline
4 medium fennel bulbs—halved, cored and thinly sliced on a mandoline
2 Granny Smith apples—halved, cored and thinly sliced on a mandoline
Three 6-ounce bunches of watercress, large stems discarded
1 cup seedless red grapes, halved
3/4 cup chopped flat-leaf parsley
In a small bowl, mix the olive oil, lemon juice and vinegar. Season with salt and pepper. In a large bowl, squeeze the 1/2 lemon over the celery, fennel and apples and toss well.
In another large bowl, toss the watercress with 1/4 cup of the vinaigrette. Add the grapes, parsley and the remaining vinaigrette to the celery, fennel and apples and toss well. Arrange over the watercress and serve.