For the soup
Combine the beets, cabbage, fennel, garlic, ginger, and stock in a large soup pot. Bring to a boil, cover, and simmer until the vegetables are tender. Strain the soup through a large-holed sieve. Puree the vegetables and a small amount of stock in a blender until smooth. Use the remaining stock to adjust the consistency of the soup. Season the soup with salt and pepper. Chill the soup. The soup is ready to serve once it is completely cooled. Serve the soup hot or cold and garnish each portion with 15 mL yogurt and a few fennel springs.