Melt butter in heavy large pot over medium heat. Add carrots and onion; sauté until onion is soft, about 8 minutes. Add broth; cover and bring to boil. Reduce heat, uncover, and simmer until carrots are tender, about 10 minutes.
Working in batches, puree soup in blender until very smooth. Return soup to pot. Stir in orange juice, brandy, and chopped tarragon. Simmer 5 minutes for flavors to blend. Season to taste with salt and pepper. Garnish soup with tarragon sprigs and serve.