Finely chop the onion, garlic and celery.
Peel and dice the carrot and sweet potatoes.
Heat the oil in a large saucepan over medium heat. Gently cook the onion, celery, rosemary, pancetta and garlic, for 10 minutes, stirring.
Add the sweet potato and carrot pieces. Stir for a couple of minutes, then add 1 litre stock, the lentils and chopped tomatoes.
Bring to the boil, then gently simmer, covered, for 20-25 minutes or until the veggies are tender. Add the cabbage and cook for 5 more minutes under cover. Add more stock if the soup is too thick for your liking.
Ladle the soup into serving bowls, add a dash of vinegar or a dollop of crème fraîche and top with chopped parsley.