Heat the oil in a large pan, then add the onion and garlic and fry gently until the onion is translucent. Add the chopped beetroot and juices along with the stock and simmer for 5-7 minutes.
Take the pan off the heat and let cool slightly, then use a hand-held blender to whizz to a purée until smooth. Return to the heat to warm through
Combine the soured cream and horseradish sauce in a small bowl. Ladle the soup into 4 bowls, swirl in a spoonful of the sauce, garnish with dill and serve.