Peel the celery and cut into very fine strips. Peel and quarter the apples, remove the core and also cut into very fine strips. Finely chop the walnuts, except for a few to garnish. Season the mayonnaise with salt, whip the cream until stiff and fold in. Mix all ingredients with the sauce, place in a salad bowl and garnish with the remaining walnuts. The salad should sit in a cool place for about 2 hours.