Apple and Celery Salad with Peanuts

2 tablespoons fresh lemon juice
1/2 teaspoon Dijon mustard
1/4 cup olive oil
3 crisp red apples, cut into 1/4" thick julienne
2 tart green apples cut into 1/4" thick julienne
4 large celery ribs, cut into 1/4−inch−thick julienne
1/4 cup chopped fresh parsley
1/3 cup dry−roasted peanuts, coarsely chopped

Whisk together lemon juice and mustard in a large bowl. Add oil in
a stream, whisking until emulsified. Add apples, celery, and parsley,
tossing to coat. Just before serving, sprinkle with peanuts.