First make the dumplings. Cut off any rind from the bacon and keep to add to the soup for extra flavour. Finely mince the bacon in a food processor (if it is too coarse, the dumplings will fall apart). Mix the bacon together with the garlic, parsley and cheese in a bowl and season with salt and pepper. Divide the mixture into 12 and shape into small balls about the size of a walnut, pressing them together firmly with your hands. Cover with cling film and put in the fridge until needed.
To make the soup, heat the rapeseed oil in a large saucepan. Put in the onion and the reserved bacon rind and fry over a low heat until soft. Add the carrot and fry for 2 minutes. Add the fennel and fry for another 2 minutes, adding more oil if needed. Next add the celeriac and celery to the saucepan and fry for 1–2 minutes.
Add the thyme sprigs, then pour in the stock and bring to the boil. Next drop in the dumplings and gently simmer, without boiling, for about 4 minutes. Remove the thyme sprigs and the bacon rind to serve. Check the seasoning.
Garnish the soup with more picked or chopped flat-leaf parsley, some celery leaves and a grating of Parmesan cheese. Delicious served with some crusty bread.