Preheat the oven to gas 2½, 160°C, 140°C fan. Untie the chicken, then put the halved onion and a sprig of sage into the cavity. Loosely re-tie the legs with string. Combine the bacon and chopped sage. Carefully push your fingers between the skin of the breast and its meat to make a pocket, then stuff with the bacon and sage mix. Smooth the skin back down and then season generously.
Heat ½ tbsp oil in a nonstick frying pan, then brown the chicken all over for about 10 minutes, using wooden spoons to help turn and balance it as you cook the sides. Transfer to a large casserole or baking dish.
Add ½ tbsp oil to the pan, soften the chopped onion, then spoon around chicken. Fry the mushrooms for 5 minutes over a high heat, then add to the casserole.
Splash the wine into the pan, boil down to about 1 tbsp, then add the stock and bring to the boil. Pour this around the chicken. Cover the pan, then transfer to the oven for 1½ hours.
Uncover the pan and turn the oven up to gas 6, 200°C, 180°C fan. Roast the bird for another 30 minutes or until golden and the juices run clear from the thickest part of the thigh. Stir the cream into the mushroom sauce at the bottom of the dish, then rest the bird for 10 minutes. If you like, fry a few sage leaves till crisp, drain, then scatter over the chicken. Serve with some steamed broccoli or other greens.
Make it in a slow cooker
Follow the recipe as above, using 150ml stock instead of 250ml. Cover and cook on Low for 7 hours until the chicken is cooked through. Stir in the cream and finish with the crisp sage, if using.
If you don’t have a hob-to-oven casserole dish – simply fry the meat or veg in a frying pan first, then transfer to a large baking dish. Make the saucy element in the same pan, then combine. Cover the baking dish with foil instead of a lid and cook as above.