In a large bowl, toss the celery root, apple, and onion. Mix together the mayonnaise, sour cream, pure wasabi powder, vinegar, honey, green onions, salt, and pepper in a separate bowl and then add to the celery root mixture. Toss to combine. Cover with plastic wrap and refrigerate for at least one hour for the flavors to marry.
Can be made the night before
Recipe courtesy of Janet Johnston