Heat half the oil in a large saucepan over medium heat. Add beef. Cook, stirring, for 5 minutes or until browned. Transfer to a bowl. Heat remaining oil in same pan. Add onion and garlic. Cook, stirring, for 3 to 4 minutes or until softened.
Return beef to pan with beetroot, potato, celery, stock, vinegar, bay leaf and 2 cups water. Bring to the boil. Reduce heat to low and simmer, covered, for 1 hour. Discard bay leaf. Cool for 10 minutes.
Remove beef from soup. Shred beef u sing two forks. Using a stick blender or food processor, process warm soup until smooth. Season with salt and pepper. Ladle soup among serving bowls. Serve topped with shredded beef and sour cream.