Preheat oven to 325 F. Remove any beet tops and excess root then thoroughly wash beets and pat them dry. Lightly coat the beets in canola oil and season them liberally with salt. Wrap the beets together and in a single layer in an aluminum foil packet. Take care to seal the packet well as the steam generated will help cook the beets and prevent them from drying. Place the beets in the oven to bake. Due to variations in the size of the beets, cooking times may vary. Check the beets after 1 hour by piercing the beet with a paring knife. the knife should easily penetrate through the flesh of the beet with very little resistance. If the beet is still not cooked, continue baking until tender. Baking at the low temperature helps to preserve the color by preventing caramelization. Once the beets are cooked, remove them from the oven and allow them to cool to the point where you are able to comfortably handle them, but they are still warm. Use a paper towel to help slip off the skins from the beets. Use a paring knife to remove any stubborn skin. Dice one and a half whole beets into small wedges or cubes and set aside for the garnish. The remainder of the roasted beets will be coarsely chopped for the soup.
While the beets are baking, add the Canola oil to the All-Clad 3qt sauce pot and place over medium low heat. add the onions, cabbage, garlic and salt. Sweat the vegetables until they are fully softened while stirring frequently, do not allow the vegetables to color. Once the vegetables are completely soft, add the tomatoes and roasted beets. Add the water and bring to a gentle simmer. Continue to cook for another 15 minutes. Add the vinegar, sugar and adjust the salt seasoning if necessary. Use the All-Clad Immersion Blender to blend the soup to your desired consistency. This soup is great left slightly chunky for a rustic texture or if more refinement is desired, puree the soup completely and pass it through a fine mesh strainer. Chill the soup completely before serving.
For the garnish place the cucumbers and radishes in a small mixing bowl and sprinkle them with salt then refrigerate for about 15 minutes. The salt will slightly wilt the vegetables and release some excess moisture. Drain off the excess moisture.
To plate the soup, add a couple small cubes of avocado to the base of the chilled serving bowl. Dress the roasted beets, cucumbers, radishes and shallots with extra virgin olive oil, lemon juice and then season lightly with salt. Arrange the dressed vegetables attractively around the yoghurt. Garnish with the pumpernickel croutons and dill sprigs. Pour the soup over the garnish just before serving to your guests.