Place the onions, garlic and bacon in a large saucepan and fry for 2–3 minutes.
Add the sweet potatoes, parsnips, thyme and stock, bring to the boil and simmer for 15 minutes.
Transfer two-thirds of the soup to a liquidizer or food processor and blend until smooth. Return to the pan, add the cabbage and continue to simmer for 5–7 minutes until the cabbage is just cooked. Serve with Irish soda bread.