Step 1

Take the chicken out of the fridge, remove the wrapping and put it in a roasting tin. Preheat the oven to 200ºC, gas mark 6.

Step 2

Make the stuffing. Melt the 20g butter in a sauté pan and gently fry the onion and celery for 4-5 minutes, until soft but not coloured. Add the garlic and cook for 2 minutes more. Remove the coarse stalks from 80g of the watercress – use them for soup – and roughly chop the leaves. Add to the pan and heat until the watercress has wilted. Put in a big bowl and leave to cool. Add the remaining ingredients, mix together and season generously.

Step 3

Remove any fat from around the small neck cavity of the chicken, then fill with a small handful of the stuffing, being careful not to overfill it. Return the skin to seal in the stuffing, then secure with a cocktail stick if needed. Spoon the remaining stuffing into a buttered ovenproof dish (about 25x15cm) and dot the top with a little butter. Cover and chill until ready to cook.

Step 4

Spread the 15g butter over the chicken breast and legs. Season well. Roast for 1 hour, then lower the heat to 180ºC, gas mark 4 and cook for 45 minutes more, putting the dish of stuffing into the oven and cooking it for the final 30 minutes. The chicken is ready when you pierce the skin between the leg and the body, and the juices run clear, with no pink meat. The stuffing should be piping hot and golden. Transfer the bird to a large warm plate, cover with foil and insulate with tea towels. Leave it to rest for 15 minutes. Keep the stuffing warm too.

Step 5

Meanwhile, set the roasting tin on the hob and add the vermouth, stirring to scrape up everything on the base, and boil for a few minutes. Transfer to a glass jug. Throw some ice cubes in to send the fat to the top. Lift off any fat you can see and keep it.

Step 6

Sauté the shallot in some of the chicken fat in a medium saucepan, until soft but not coloured. Add the juices from the chicken and the chicken stock. Bring to the boil, then turn down to a simmer and reduce until you like the flavour – don’t think about the thickness, just the flavour. Strain and transfer to a warm jug.

Step 7

Unwrap the chicken. Add the remaining clump of watercress to the plate and serve with the stuffing, gravy and vegetables.