Preheat oven to 400 degrees F.
Trim beets, leaving 1-inch of stems attached, and scrub well. Wrap beets tightly in foil and roast in middle of oven until tender, about 1 1/2 hours. Unwrap beets carefully and let stand until cool enough to handle. Peel beets. Cut half of 1 beet into 1 inch long match sticks for garnish and chop remaining beets.
In a large heavy saucepan heat oil over moderate heat until hot but not smoking and cook onions with fennel seeds, stirring, until softened, about 15 minutes. Add sliced fennel and water and cook, covered, stirring occasionally, until fennel is very soft, 15 to 20 minutes. Stir in chopped beets and broth and simmer, uncovered, 15 minutes. In a blender puree soup in batches, transferring it as pureed to another saucepan. Soup may be prepared up to this point 2 days ahead and chilled, covered. Reheat soup until hot, thinning with water if necessary. Stir in orange juice, liqueur if using, and salt and pepper to taste.
Garnish soup with beet match sticks and fennel leaves and serve with bread sticks