1. Preheat oven to 400°. Wrap the beets in foil and roast until tender when pierced with a fork, about 1 hour. Cool the beets and peel. Cut half of 1 beet into small cubes and set aside for the garnish. Chop the remaining beets into ½-inch pieces.
2. Melt the butter with the oil in a heavy medium-size saucepan over medium-high heat. Add the leeks, onion and celery and cook until they begin to brown, stirring frequently. This should take about 15 minutes. Stir in ginger, allspice, white pepper and beets. Cook, stirring, until the vegetables begin to stick to the bottom of the pan, about 5 minutes. Add 4¼ cups water, the bay leaf, thyme and parsley. Bring to a boil. Reduce heat to low, cover and simmer until the vegetables are very tender, about 25 minutes. Remove the bay leaf, thyme and parsley.
3. To purée the soup, fill a blender or food processor no more than halfway. Start on low speed, keeping
your hand on top in case the lid pops off from the rising steam. Increase the speed to high and blend until smooth, about 1 minute. You might need to do this in batches.
4. Return the soup to a clean pot set over low heat. Add the cream and salt and pepper to taste. Stir well.
5. Ladle into soup bowls. Garnish each serving with the reserved beet cubes and 1 tablespoon of cream, if desired.