This refreshing--and refreshingly easy--soup would be perfect for lunch or as a starter for a summer dinner party. The recipe calls for cooked, peeled beets, which you can find in vacuum-packs at most supermarkets, or you can boil or roast beets and then peel them before using. The only other ingredients are tomato juice and celery, which are blended along with the beets until silky smooth, and fresh parsley and sour cream or creme fraiche for the garnishes.