1.Melt half the butter in a large frying panover medium heat; cook onion, stirring, until soft. Transfer onion to a 4.5-litre (18-cup) slow cooker.
2.Melt remaining butter in same pan over medium-high heat; cook beef, stirring, until browned all over. Transfer beef to slow cooker. Add the water to same frying pan; bring to the boil, then add to slow cooker with beetroot, potato, carrot, tomato, stock, vinegar and bay leaves. Cook, covered, on low, 8 hours.
3.Discard bay leaves. Remove beef from soup; shred using two forks. Return beef to soup.
4.Stir cabbage into soup; cook, covered, on high, about 20 minutes or until wilted. Stir in parsley. Season to taste.
5.Serve soup topped with sour cream.
Recipe is suitable to freeze at the end of step 3. Thaw overnight in the refrigerator; reheat then continue from step 4.