The night before you want to cook, remove all the packaging from the chicken and pat dry using kitchen paper. Sprinkle the sea salt all over the chicken, inside and out, then put on a baking tray or in a baking dish. Keep chilled, uncovered, overnight. (This will help the skin crisp up during roasting.)

The next day, bring the chicken to room temperature while you make the stuffing. Melt the butter in a frying pan over a medium heat until foaming, then add the oil. Fry the leek for 8 mins until softened, then stir in the garlic, wine, thyme leaves and sage. Simmer until most of the liquid has evaporated. Remove from the heat, season, set aside and leave to cool for a few minutes.

Butter a baking dish. Mix the breadcrumbs, parmesan, eggs and watercress together in a large bowl. Season, then add the lemon zest and a squeeze of lemon juice. Stir in the softened leek mix and transfer to the prepared baking dish. Drizzle over a little oil and cover with foil.

Heat the oven to 220C/200C fan/gas 7. Put the potatoes in a large roasting tray. Drizzle over a little oil, then toss with some seasoning to coat. Pat the chicken dry again using kitchen paper, then rub a little oil into the skin. Season with black pepper, then nestle the chicken into the middle of the tray, among the potatoes. Put the lemon halves and thyme sprigs into the chicken cavity and roast for 30 mins.

After 30 mins, put the stuffing on the oven shelf under the chicken and reduce the oven temperature to 200C/180C fan/gas 6. Baste the potatoes in the chicken juices, but don’t baste the chicken or the skin won’t crisp up. Roast for 30-45 mins more until the chicken is cooked through – a meat thermometer should read over 70C or the juices should run clear when pierced with a knife in the thickest part. Remove the foil from the stuffing halfway through cooking to crisp up the top.

Leave the chicken to rest, uncovered, for 15-20 mins. Scoop the potatoes into a warmed bowl. Remove any excess fat from the roasting tray using a spoon, then tip the roasting juices into a pan and bubble with a splash of wine, the chicken stock and cornflour mixture until it has thickened slightly and you have a light gravy. Serve the chicken with the potatoes, stuffing and gravy.