How to Make It
Preheat the oven to 400°. Toast the walnuts in a pie plate for about 6 minutes. Let cool and coarsely chop.
In a small bowl, whisk the egg yolk with the vinegar. Slowly drizzle in the walnut oil, whisking until the vinaigrette begins to thicken. Slowly whisk in the remaining walnut oil until incorporated. Whisk in the cream and season with salt and pepper. Stir in the walnuts.
In a large bowl, combine the apple with the celery root. Add 1/2 cup of the vinaigrette and toss well. Transfer the salad to a platter or plates. Arrange the smoked trout fillets on top and spoon some more of the dressing on the trout. Sprinkle with the chives and serve