Preheat the slow cooker if necessary; see the manufacturer's instructions. Heat the oil in a large frying pan, add the onion and fry, stirring, until softened. Add the vegetables, fry for 1–2 minutes, then stir in the paprika, chillies and caraway seeds and cook for 1 minute.
Stir in the flour, then mix in the canned tomatoes and stock, add the bay leaves and a little salt and pepper and bring to the boil. Transfer to the slow cooker pot and press the vegetables below the surface of the liquid. Cover with the lid and cook on high for 4–5 hours or until the root vegetables are tender.
Stir the goulash and discard the bay leaves. Spoon on to plates and top with spoonfuls of soured cream and a sprinkling of extra paprika, if liked. Serve with plain boiled rice.