Heat half the oil in a large heavy based saucepan or casserole dish over medium-heat. Add the oxtail and cook for 8 to 10 minutes, turning, in batches if necessary, until browned. Transfer to a plate and set aside. Add the remaining oil, garlic, onions, carrot and celery to the pan, and cook for a further 8 to 10 minutes until softened. Add tomato paste and cook for 2 to 3 minutes. Return oxtail to the pan, add herbs, stock and 4 cups water and bring to the boil. Reduce heat and simmer, partially covered, for 3 hours, or until meat is falling off the bone, adding extra water if needed during the cooking process. Skim fat from the top of the soup during cooking. Season. Stir through mushrooms.
For the dumplings, combine the flour, chopped rosemary, parmesan, cloves and salt in a large bowl. Pour in eggs and stir to combine. Gently knead dough for 1 minute, adding a little water if required, then roll mixture into heaped teaspoon sized balls. Add balls to the soup, cover with a lid and gently simmer for 12 to 15 minutes until dumplings double in size.
Serve soup sprinkled with parsley and lemon zest with crusty bread on the side.
Use any combination of mushrooms in the soup you like – for an Asian twist, use Asian mushrooms and use coriander instead of rosemary in the dumplings.
For a healthier dumpling, you can use wholemeal self-raising flour.
Ask your butcher for nice plump pieces of oxtail to maximise the meat in the soup.