Once I've taken the meat off a cooked chicken, I chuck the carcass & skin in a big pan, I chuck in a few chunks of raw carrot, an onion, cut in half, a couple of bay leaves. Cover with boiling water, put the lid on the pan & let it simmer for 2 hours or so. Sieve the liquid into a jug, cool & then leave in the fridge overnight. Next day skim the solidified fat off, put the rest of the jelly/stock into plastic containers & freeze.