Place the leftover bones and skin of a roast chicken or raw chicken carcass in a large pot with celery, onions, a few cloves of crushed garlic, parsley, a bay leaf, and salt and pepper. Add water until everything is covered, then bring to the boil. Reduce heat, and leave to simmer partially covered for four hours. Scoop off foam periodically, and strain the stock through a sieve at the end.
Leeks, shallots and turnips are other vegetable options. Customize your stock by adding your favorite herbs, or any you have left over in the refrigerator. Rosemary, oregano and thyme work well. A small handful of black peppercorns can add bite.
If you plan to use the stock for a soup, simmer for an hour or two longer to make it more concentrated. Leave the stock to cool for 30 minutes before saving it in the refrigerator. Do not scoop the fat off the top, as it forms a barrier between the stock and the bacteria in the air. Leaving the fat makes the stock last longer. For low-fat recipes, pour the stock out from under the fat layer.
Chicken stock lasts around four days in the fridge, so portion and freeze what you're not using immediately. Frozen stock is good for two to three months.