Place marrow bones, oxtail and chicken wings in a colander and rinse thoroughly.
Fill the large 7 litre capacity pot about half way with water from the tap and then place marrow bones, oxtail and chicken wings in. Top up with water so pot is completely full.
Turn on the heat and bring up to the boil. Skim off any scum/ foam that rises to the top with a spoon. Continue to skim off scum until it no longer rises to the surface (this will take at least 15 minutes). If you are scoping out too much liquid when skimming off the scum don't worry just top up with fresh water.
Once the scum has subsided add the onion, carrot, celery and parsley. Then add the tomato paste, salt and crumble in the stock cubes. If any foam rises during this process skim it out.
Cover the pot with a lid and simmer for 4 hours.
After 4 hours turn off the heat and remove the bones, meat and vegetables with some tongs. Then strain the broth through a fine sieve into the other pot.
Allow the broth the cool to room temperate and then place in the fridge overnight.
The next morning a layer of solidified fat should have formed on the surface of the broth, use a spoon to carefully skim it off the top.
After you have skimmed off the fat put the Brodo on the heat until it reaches a boil, then turn off and serve.