Heat oil in a large stock pot over medium-high heat and cook onion for about 5 minutes until soft. Stir in carrot and cook for another 5 minutes. Stir in celery root and red pepper and cook 1 minute.
Add turnips, vegetable stock or water, chili pepper if used and bring to boil. Reduce heat and simmer for about 20 minutes until vegetables are tender. Stir in rice.
In a large bowl mix sour cream with egg yolk, add 2 ladles of hot soup, stir well and add to the pot. Let boil for 1 minute then add parsley, salt and pepper. Remove from heat.