Cook the lentils and rice in boiling water for approx. 10 mins. until almost soft, then drain.
Chop the shallot, press the garlic, sauté both in the oil. Dice the beetroot, add to the pan and briefly sauté. Add the stock and balsamic, bring to the boil, cover and simmer over a low heat for approx. 15 mins. Puree the soup, return the lentils and rice to the pan, gently heat through, season.
Blend the sour milk and horseradish with a handheld blender until frothy. Serve the soup in bowls. Finely chop the parsley and sprinkle on top of the soup.
Serve with wholegrain bread.