Sweet potato is an easy-to-digest source of carotenoids, which supply vitamin A.
A regular intake of fermented foods like bio yogurt is good for the gut (where 60 per cent of our immune defences are), and may increase our resistance to viral and bacterial infection.
Heat the oil in a large pan, add the onion and garlic, and fry for 5 mins until starting to colour. Stir in the beef, increase the heat and fry, stirring, to brown it.
Add the caraway and paprika, stir well, then tip in the tomatoes and stock. Cover and leave to cook gently for 30 mins.
Stir in the sweet potato and green pepper, cover and cook for 20 mins more or until tender. Allow to cool a little, then serve topped with the yogurt and parsley (if the soup is too hot, it will kill the beneficial bacteria in the yogurt).