Serve hot or cold, anytime when turnips are in season.
Combine turnip, carrot, potato, and stock in soup kettle. Bring just to a boil, reduce heat, and simmer, partially covered, 30 minutes or until turnip is tender. Press vegetables and liquid through food mill. Return mixture to kettle and heat. In separate bowl combine cream and egg yolk and beat lightly. Add ½ cup hot soup liquid to cream mixture and blend with whisk. Return mixture to kettle. Stir until smooth. Season with salt and pepper. Garnish with chopped parsley and thinly sliced tomato.