Preheat oven to 200°C (400°F/Gas 6). Roast beef bones in 2 large roasting tins for 1 hour or until golden. Remove from oven and combine in one roasting tin. Strain rendered fat from the empty tin, add vegetables and roast for 30 minutes or until golden. Transfer bones and vegetables to a stockpot, add peppercorns, bay leaves, thyme, pig’s trotter and enough water to cover. Bring to the boil over high heat, then simmer, occasionally skimming any scum from surface, over very low heat for 7 hours. Strain through a fine sieve, then strain again through a fine sieve lined with muslin (cheesecloth). Cool, then refrigerate for 2–3 hours or until the fat has separated from the stock, then skim solidified fat from the top and discard. Strain the stock into a saucepan, put it over medium–high heat and reduce the stock to sauce consistency, about 20–30 minutes.