To prepare the poultry seasoning, place all of the ingredients in a blender and blend until it forms a fine powder. Store in an airtight container.
Remove chicken from the refrigerator and bring to room temperature as you prepare the stuffing.
Preheat the oven to 200C/ 180 C fan/ 400F and move the middle rack to the lower third of the oven.
Heat 1 tbsp of the olive oil in a saute pan and gently fry the one finely chopped onion for 5-7 minutes until it begins to soften and become transleucent.
Remove from the heat and place the onion in a medium sized mixing bowl to cool to touch.
Add the torn bread, the poultry seasoning, sultanas and season well to taste. Add enough of the remaining olive oil to bind everything together. Use your fingers to squeeze it all together.
Carefully remove some of the elastic holding the chicken legs together (don't remove it entirely as you'll put it back afterwards) and stuff the chicken cavity with the stuffing. Use the elastic to tie the legs back together and place the stuffed chicken in a large roasting tin.
Mix the softened butter and the chopped herbs together and, using your fingers, lift the skin over the breasts and place 1/3 of the herb butter under the skin on either side, taking care not to tear the skin. Rub the remaining herb butter over the outside of the chicken skin.
Cut the garlic bulbs in half, leaving the paper on, and arrange in the roasting tray. Scatter the remaining onions, quartered, in the roasting tray too, and pour in the water.
Cover the chicken and the tray tightly with foil so that the steam can't escape. Roast for one and a half hours (set a timer!) without touching it. No need to baste.
Meanwhile, peel and wash your potatoes. Cut them into roast potato size and parboil them in boiling, salted water for five minutes. Drain and return to the pan. Pop the lid on and give it a gentle shake so that the edges roughen up a bit.
Preheat your top oven (or if your oven is big enough, pop them under the chicken), to 220 C/ 200 C fan.
Preheat your roast potato roasting tin with your fat of choice until the fat is smoking. Add the roast potatos, shake the pan to cover the potatoes in the melted fat and return to the oven for 45-60 minutes, turning occasionally.
Peel and chop your turnip and carrots, placing them together in a small saucepan. Cover with water and gently simmer for 25 minutes or so until tender. Reserve the cooking water. Mash the cooked vegetables with the butter and freshly grated nutmeg. Keep warm.
Remove the foil from the roast chicken and carefully drain off all the cooking liquid into a small saucepan. I find it's easier to remove the chicken to a waiting plate first, and then return it to the roasting tin.
Pop the chicken back into the oven for another 20 minutes or so, until the skin is browned nicely.
Meanwhile, using a handblender, blend the cooked quartered onions with the roast chicken cooking liquid and the stock cube (if using) until smooth. Return to the saucepan, add enough of the turnip/carrot cooking liquid to bring it up to a pint and bring to a simmer. Add the cornflour dissolved in a little water and stir the gravy until thickened. Use more cornflour if you prefer a thicker gravy. Keep warm.
If you want to keep the calorie content of the stuffing lower, use water instead of the olive oil to bind everything together.Leftover reheat very well, simply arrange in a casserole tray, cover and reheat at 200C for 30 minutes or so.Freeze leftover roast chicken and leftover gravy for another day.