Heat the beef dripping or olive oil in a stockpot or a very large saucepan. Add as many bones as will ﬁt in a single layer in the bottom of the stockpot and cook them on low heat in batches until they are a rich brown all over. Take care not to let the fat burn. Remove each batch from the stockpot and set aside.
Add the onions to the stockpot and cook slowly until they are a rich brown. Return the bones to the pot and add the meat, chicken and water. Heat very slowly until the water comes close to the boil, then add a cup of cold water and reduce the heat. Skim any scum from the surface, then add the prepared vegetables, herbs and peppercorns. Partly cover the stockpot with a lid and simmer over low heat for 5–6 hours, skimming the scum frequently from the surface of the stock.
Remove the stockpot carefully from the heat. Line a large colander with a piece of muslin or a clean tea towel. Strain the stock through the prepared colander into a very large bowl or jug. Discard all the bones, meat and vegetables. Cover the stock with a piece of muslin or a net cover and allow to cool. Once cold, refrigerate overnight. Next day, carefully discard the solidiﬁed fat from the surface. The stock can be frozen in measured quantities for later use.