1. In a 6-quart pot over medium heat, melt butter. Add beets, apples, onion, and garlic; cook 6 minutes. Stir in wine and syrup; simmer until reduced by half. Add stock and bring to boil. Lower heat to simmer; cook until beets are tender, about 1 hour.
2. Purée soup in a blender. Season with salt and pepper. Serve garnished with sour cream and tarragon.