Borscht (Beet Soup)

2 cups peeled beets (boil enough to loosen skins)
1 1/2 cups carrots
1 cup onion
1 tbsp butter
2 cups vegetable or meat stock
1 cup shredded cabbage
1 tbsp vinegar
salt and pepper

Cube or chop beets, carrots, and onions, and simmer for 20 minutes in stock. Add rest of ingredients and simmer another 20 minutes. Serve with sour cream, cottage cheese, or yogurt.