First of all mix the olive oil with the lemon juice, then place the pork chops in the roasting tin with the chopped onion tucked amongst them.
Season with a little salt and freshly milled black pepper, then brush the chops with the oil and lemon juice. You can, if you like, do this well in advance, just cover with a cloth and leave in a cool place. Then, when you're ready to cook the pork chops, pre-heat the oven to gas mark 6, 400°F (200°C), then pop them 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 red wine, stir it into the sauce and let it bubble for about 1 minute. Then serve the pork chops on a bed of Very Red Rice with the sauce spooned over and garnish with the sprigs of watercress.