You want as little moisture and odour as possible to escape from this simple but intoxicating dish. The idea is that you lift the lid from the pot at the table, releasing a rush of garlicky vapour. In my favourite cookbook, Richard Olney (scroll down to find him) recommends making a flour and water paste, which you form into a thin sausage shape and place over the rim of the pot: it makes a seal when you clamp on the lid. On the couple of occasions when I have tried this method, I have found that the lid -- which I may have clamped on too firmly -- has squeezed the pastry from the rim, rendering it entirely ineffective. Still, the lid of a Le Creuset fits quite tightly.
I used a whole, Label Anglais chicken. The advantage is that it is of higher quality than the thighs and drumsticks you can buy separately; the drawback is that the breast cooks for longer than is necessary, and may dry out and toughen. You could, if you were prepared to break the rule about lifting the lid of the pot, add the breast portions half an hour from the end.
Richard Ehrlich, in his engagingly helpful The Perfect . . . (also published by Grub Street, and featured on the page that advertises Olney's Simple French Food), says that you need "an absolutely disgraceful quantity" -- up to 300 ml -- of olive oil, in which the garlic cloves can stew. I am happy to let them steam.
The timings here suit my oval Le Creuset, which takes a long time to heat up. They also suit my taste for meat that falls off the bone -- but are not ideal for the breast meat.
1 chicken, cut into 8 pieces
4 heads garlic, separated into cloves
3 tbsp olive oil
Herbs: rosemary, thyme, tarragon (according to taste)
Toss the ingredients in a casserole. Bake, covered, at gas mark 4/180 C for one hour; and then at gas mark 1/140 C or lower for a further hour.