Prepare beets by washing and then cutting off leaves about 2 inches above the beet, also leaving the root intact. Place in large saucepan with enough water to cover and bring to a boil. Turn down heat to just boiling and cook until beets can be easily pierced with a knife (start with about 35 to 40 minutes) Drain and rinse with cold water to cool. Slip off the skins, leaf stems and root and discard. Cut into 3/4 inch chunks and set aside in a bowl for use later. Reserve a few small cubes per bowl separately for garnish if desired. (This step can be done ahead or while you are making the soup. It is at your convenience. Just store the cooked beets covered in the fridge if doing this the day before)
While beets are cooking, in another large saucepan or small Dutch oven, melt butter and saute onion, celery, carrot, cabbage (and shredded potato if using)until softened and translucent. Add turmeric and/or saffron and stir in well. Add stock and soup (or fresh tomatoes) Stir in potato flakes now (if using instant flakes). Add bouquet garni and bring to a boil, turn down heat to medium or medium low and simmer stock, veggies and seasoning for 30 minutes. Add Beets and continue to simmer for another 15 minutes.
Remove soup from stoveand remove the bouquet garni and discard. Process soup until smooth. ( You have several choices for method: blender, food processor, immersion stick blender or food mill) Take care with the hot soup to assure you do not get burned by steam or splashing soup. Each method will give you a slightly different texture. I used a food mill to remove all lumps. Add sweetener (if desired), vinegar and hot sauce (optional) Stir well and adjust seasoning to your tastes. If the soup is too thick, thin with a little more stock. If too thin, stir a few more tablespoons of potato flakes into a half cup of warm water and add to soup to thicken.
Serve with a dollop of sour cream and some chopped fresh dill weed, or swirl in some sweet cream and sprinkle with chopped dill or parsley and a few reserved beet cubes.