Mix the egg yolks and 1 teaspoon lemon juice in a mixing bowl. Beat the oil first drop by drop, then in a thin stream until a creamy mayonnaise is obtained.
##Whip the cream with the whisk of the hand mixer until semi-stiff and fold into the mayonnaise. Season with salt and pepper.
##Celery## peel and slice on a vegetable slicer with a julienne slice into thin sticks or first cut into thin slices, then into sticks. Stir immediately into the mayonnaise.
##Apples## wash, quarter and core them. Also slice or cut them into thin sticks and immediately fold them into the celery salad - so they don't get brown.
Finely chop the walnuts and fold into the salad. Season with salt, pepper and sugar. Cover and leave to stand for about 1 hour. Then season again.