Cut the pork into 1 inch cubes. In a soup pot add the 8 cups of water and add the pork and the celery root to the water. Boil on medium heat for 45 minutes. To keep the soup clear, make sure you skim the gray foam that forms at the top of the soup during the first 15 minutes of boiling.
In a large skillet add olive oil, chopped onion, shredded carrot, celery, shredded parsnip and chopped pepper and cook on low heat for about 10 minutes, just until the vegetables soften up a bit.
Add the vegetables to the soup , and season with salt and pepper. Simmer for another 15-20 minutes on low heat, so as not to boil the soup again.
Remove the celery root from the soup.
Add uncooked rice to the soup and continue cooking.
In a bowl, whisk the sour cream with the flour together and add a couple ladles of the hot soup to the bowl to thin out the sour cream mixture. Pour the cream slowly into the soup pot, stirring constantly so as not to curdle.
Add the tarragon and lemon juice and let it cook for another 10 minutes on low heat. You may want to taste for salt and pepper at this time and add more if needed.
Sprinkle with fresh parsley and serve hot with hot peppers on the side.