Cut the onions, carrots, and beets and sauté over medium heat in the olive oil with a pinch of salt in a large soup pot.
Reserve a small amount of beet to grate and add near the end to enliven the color.
Bring the vegetable stock to a boil. When the vegetables are soft , add the shredded cabbage and the hot stock.
Bring to a boil and simmer 15-25 minutes, until the vegetables are tender. With a few minutes left, add the reserved grated beet.
Season to taste with salt and pepper, then squeeze in the lemon juice, aiming for a pleasing but subtle sour taste.
Serve with freshly grated black pepper, a dollop of sour cream, and chopped parsley, if desired.