Heat the oven to 220C/fan 200C/gas 7. Tip the beef bones, chicken wings and all the vegetables onto a large roasting tray and roast for 1 hour until really crisp and browned.
Carefully pour off some of the fat from the tray into a ramekin, then tip all of the vegetables and bones into a large pan with the black peppercorns, thyme, and 1.5 litres of cold water, making sure to really scrape the roasting tray to include any crusty bits off the bottom.
Bring to a gentle boil and leave to simmer for 1 hour 30 minutes, using a wooden spoon to break up the wings during cooking to release more gelatin. Skim any fat or impurities from the top every now and again. Strain through a fine sieve into a bowl or container, using a ladle to squeeze all of the liquid out of the meat and bones. At this stage, you can cover, chill or freeze the stock for future use, or use straightaway.
Heat a large, deep frying pan over a medium heat and add the red wine and bubble until reduced by a third. Pour in the strained stock and simmer gently for 45 minutes, skimming regularly, or until the sauce has thickened and is looking glossy.
Mash together the softened butter and plain flour until smooth, then whisk into the gravy, then simmer for 15-20 minutes or until thickened. Season and serve.