Bones are the heart of a good stock, and those that still have some meat attached will result in much more flavour. Beef bones are available from the butcher and some supermarket meat counters, and chicken bones from the carcass left over from a roast can be used. Using the skin is not recommended, as it will produce greasy and cloudy stock. For meat stock, the bones are first roasted in the oven, uncovered, until browned. Any vegetables being used can be roasted alongside for an even richer flavour. The bones and any trimmings are placed in a pan of cold water with the vegetables and herbs before bringing to the boil, uncovered. The heat is then reduced and the stock simmered, still uncovered, for 1-2 hours for chicken stock and 4-6 hours for beef. The bones are removed once the stock has finished cooking, any solids strained out and the liquid poured into a bowl and placed in the fridge. Once chilled, the solidified fat on top can be scraped off and discarded. The stock can be kept in the fridge for up to 2 days and frozen for up to 3 months.