Heat the oil, add the onion and sauté gently, then add the garlic and caraway seeds. Cook for a further 3 minutes, stirring occasionally. Add the beetroot, potato, cider vinegar and stock, cover and simmer for about 1 hour, until the beetroot is tender.
Season to taste, allow to cool slightly, and then puré in a food processor or blender.
Return to the pan, reheat and garnish with a swirl of sour cream or Greek yoghurt before serving.