Pat the oxtails dry with paper towels and remove as much visible fat as possible. Using a sharp, heavy knife, cut the oxtails into sections (or ask your butcher to do this for you). Place the oxtail in a stockpot and cover with plenty of cold water. Cover with a lid and bring to the boil over medium heat. Turn the heat off and allow the oxtail to stand for 20 minutes. Strain, discarding the water. Place the oxtail on a clean chopping board and pat dry with paper towels.
Melt the dripping in the stockpot over medium-high heat. Cook the oxtail, in batches, for 4–5 minutes on each side, or until browned. Remove the oxtail and set aside. Add the carrot, onion and celery and cook, stirring constantly, until lightly browned. Return the oxtail to the pot, along with the bouquet garni and bacon or bacon bones. Add the water or stock, making sure the oxtail is completely covered. Bring to the boil slowly, skimming any excess fat from the surface. Cover with a lid and simmer over very low heat for 4 hours, checking every hour that the oxtail is still covered with liquid.
Remove the oxtail to a chopping board. Strain the stock into a large heatproof bowl and refrigerate overnight. Discard the contents of the strainer. Remove the meat from the bones and shred. Refrigerate the meat overnight.
Remove the solidified fat from the surface of the soup and return the soup to the stockpot with the oxtail meat and the extra carrot, onion and celery. Bring to the boil over medium heat and cook for 20 minutes, or until the vegetables are tender. Just before serving, stir in the lemon juice and parsley and season to taste with salt and pepper. Ladle into warm bowls and serve with crusty bread.
Kangaroo Tail Soup: To make kangaroo tail soup, replace the oxtails with 1 kangaroo tail, skinned and chopped. Prepare the soup as for oxtail soup, starting from frying the kangaroo tail in dripping. It is not necessary to blanch the kangaroo tail before cooking.