Combine chicken, corn, olives, raisins, carrots, celery, and apple in a large bowl.
Stir cream and mustard together in a cup and season with sugar, salt, and pepper. Pour dressing over salad and mix to combine. Season with salt and pepper and sprinkle with parsley.
Arrange lettuce leaves and watercress on a platter and spoon chicken salad in the middle. Sprinkle shoestring potato sticks on top and press into salad. Chill until ready to serve.