In a small bowl, whisk together lemon juice, salt and pepper. Slowly drizzle in oil, continuously whisking, until dressing is emulsified. Taste and add more lemon juice and/or salt if needed.
In a large bowl, toss the dressing with fennel, apple and celery. Fold in fennel fronds or parsley and walnuts. Top with Parmesan just before serving.
Notes:
Dressing can be made the day before serving. Store in the refrigerator. Toss with salad ingredients up to 1 hour before serving.
From
https://cooking.nytimes.com/recipes/1019023-fennel-apple-salad-with-walnuts