People seem to think that making stock takes hours, well the cooking does, but not your involvement in it. It really only needs 5 minutes of your time but will provide you with the basis for another meal. If the cooking time is a problem for you on the day you have a carcass to use, just freeze it and then make stock on a day when you will be around. I often do freeze the carcass anyway and then make a larger batch of stock when I have two or three. This is especially useful if your bird did not come with giblets as you have less flavour available from one carcass. However even a single carcass will make a light stock suitable for a vegetable soup or risotto.
To make the stock all you have to do is put the carcass and giblets, excluding the liver, into a large saucepan and cover them with cold water. Add a peeled onion, a carrot, stick of celery, half a dozen whole black peppercorns, a bay leaf, sprig of thyme and a small bunch of parsley (the stalks have just as much flavour as the leaves). If you haven’t got all of these things don’t worry, they add flavour but the stock will still be better than a stock cube even if you make it with just a carcass. Other potential flavourings if you have them to hand include leeks (the greener top part is fine) and the stalks, or even skin, of mushrooms. Now put the pan on to a high heat and, as soon as it begins to boil, skim the surface with a slotted spoon to remove any scum that has floated to the top and turn the heat down so that the liquid is just simmering. This means that bubbles are breaking the surface but slowly. If you have an Aga you are probably not reading this because you will already be a regular maker of stock, but you can put the stock into the bottom oven overnight. Otherwise leave it simmering on the hob, uncovered or with the lid ajar, and check the liquid every now and again to make sure that it is not simmering too hard and to skim the scum from the surface. After about 3-4 hours you should have sufficient flavour. If you added too much liquid in the first place you can concentrate the flavour once you have strained the stock by boiling hard to reduce it. Once the stock has cooled put it into the fridge overnight.
The following morning, skim the fat from the surface with a slotted spoon followed by kitchen paper used as a blotter. Any sediment will have sunk to the bottom, so pour the stock carefully to avoid disturbing it and this bit can be left behind. If you are not using the stock straight away it is best frozen, but can be kept in the fridge for up to a week if boiled before using.