Preheat the oven to 190oC/gas mark 5. Weigh your chicken to calculate the cooking time: it needs 20 minutes per 450g plus an extra 20 minutes.
Mix the butter with the lemon zest and herbs. Push the herb butter under the chicken skin and rub any extra on the outside and on the legs and wings. Season the cavity with salt and pepper and pop in the lemon halves. Place in a roasting tin and roast in the oven according to the time you calculated in step 1, basting it two or three times while it roasts. It's done when the juices run clear.
Meanwhile, combine all the stuffing ingredients together in a bowl, then spoon into a baking dish and cook in the oven for 40 minutes while the chicken roasts.
Cook the potatoes in boiling salted water until they are cooked through and tender. Drain the potatoes well and put them back in the pot. Make a creamy mash by mashing through the butter and warm milk. Season well with salt and white pepper.
To make the gravy, strain off the excess fat from the chicken roasting tin. Warm the dish on a medium to high heat on the hob, then deglaze with the wine and scrape all the tasty bits off the bottom. Transfer the contents of the roasting tin to a small pot, then add the chicken stock and let it reduce slightly. In a seperate cup mix the cornflour with a little water, then add to the pot. Heat quickly to thicken while whisking, then strain into your sauce boat, ready to serve with the roast chicken, stuffing, mashed potatoes and corn.