First of all mix the olive oil with the lemon juice, then place the chicken joints in the roasting tin with the chopped onion tucked amongst them.
Season with a little salt and freshly milled black pepper, then brush the chicken pieces with the oil and lemon juice. You can, if you like, do this well in advance, just cover it with clingfilm and leave in the fridge. Then, when you're ready to cook the chicken, pre-heat the oven to gas mark 6, 400°F (200°C), then pop the chicken in on a high shelf and cook for 25 minutes exactly. Meanwhile, combine all the sauce ingredients in a jug and, using a small whisk, blend everything thoroughly.
Then, when the 25 minutes are up, remove the roasting tin from the oven, pour off any surplus fat from the corner of the tin and pour the sauce all over, giving everything a good coating.
Now back it goes into the oven for about another 25 minutes, and you will need to baste it twice during this time. After that, remove the roasting tin from the oven and place it over direct heat turned to medium. Then pour in the extra 2 fl oz (55 ml) of red wine, stir it into the sauce and let it bubble for about 1 minute.
Then serve the chicken with the sauce spooned over. Garnish with a few sprigs of watercress.
Menu suggestion: Serve with Very Red Rice (see below), and a green salad