1: Place the chicken on top of a piece of muslin, large enough to wrap around it, and season with salt and pepper. Put the bay leaves on top of the chicken. Break apart the cloves of garlic from one bulb, but don’t peel them. Give them a bash with the back of a knife and sprinkle them over the chicken. Wrap the chicken tightly in the muslin, then put it in a large flameproof casserole.
2: Pack hay all around the chicken and pour over half the cider. Cover the casserole and place it in the oven for 1 hour, checking occasionally that the liquid hasn’t evaporated. If it needs topping up, use the remaining cider, and then some hot water, if necessary. Pierce the muslin with a knife and stab the chicken in the thigh joint to check if the juices run clear. If not, return the pot to the oven for a further 5 minutes. Leave the chicken to rest in the pot, covered, for 45 minutes.
3: Meanwhile, peel the celeriac and rub it down with a green scouring pad to make it very smooth and rounded. Heat the rapeseed oil an ovenproof frying pan over a medium heat. Add the celeriac to the pan and fry for 10–15 minutes until it is coloured all over. Once the celeriac is nicely browned, add the butter to the pan with the thyme and the remaining garlic bulb, cut in half through the equator. Baste the celeriac in the butter, then place the pan in the oven for 45 minutes until the celeriac is tender all the way through. Baste with butter 3 or 4 times during the cooking time.
4: When the celeriac is tender, remove the pan from the oven and give a good squeeze of lemon juice over the celeriac and season with salt and pepper. Do not discard the garlic and thyme.
5: Remove the chicken from the pot and place it on a chopping board. Pass any liquid from the pot through a fine sieve into a saucepan. Add the malt extract and bring to the boil. Add the chicken stock and continue boiling until the liquid reduces to a sauce consistency. Adjust the seasoning, if necessary.
6: Unwrap the chicken from the muslin and remove the garlic and bay leaves. Use a blowtorch to brown the skin. Serve the chicken whole on a platter with the whole celeriac and with a jug of the gravy. Add the thyme and garlic from cooking the celeriac as a garnish, if you like. Let the diners carve the chicken and cut the celeriac themselves.