Heat olive oil in large saucepan and fry leeks and celery for 2-3 minutes until softness, then add the beets, potatoes and carrots.
Pour vegetable broth to saucepan, season and bring to a boil, then reduce the heat and simmer, stirring occasionally, about 40 minutes or until vegetables are tender and soup slightly thickens.
Season soup to taste, then add vinegar and sugar. Gently heat until the sugar has dissolved.
Pour cooked soup in bowls and serve with sour cream.