1) Place the turkey breast between 2 sheets of cling film and pound lightly with a meat mallet to an even thickness of about 2-cm. Set aside whilst stuffing is prepared.
2) Preheat the oven to 190C/Gas 5.
3) Place the cranberries in a small saucepan and cover with water. Bring to the boil, cook for 1 minute, then remove from heat, drain and reserve.
4) Heat 2 teaspoons oil in a large heavy skillet over medium heat. Add the diced onions and cook, stirring, until onions are golden but not charred, about 12 to 15 minutes. Add the garlic and cook an additional 2 to 3 minutes.
5) Add bread, cranberries, pecans, 2 tablespoons fresh or 2 teaspoons dried sage and 125 to 190ml chicken stock, depending upon consistency of stuffing; (you want the mixture to be moistened, but not too wet, as the turkey will release moisture when cooked). Cook over low heat for about 2 to 3 minutes, remove from heat.
6) Salt and pepper the inside and outside of the turkey breast. Spread the stuffing on the turkey, leaving about 3 to 5cm uncovered on all sides. Roll up and secure tightly with kitchen twine, trying to keep all stuffing intact.
7) Heat 1 tablespoon of rapeseed oil in a large Dutch oven or medium-sized roasting pan until hot. Sear stuffed turkey breast on all sides until lightly browned, 3 to 4 minutes per side.
8) Add sliced onion and 375ml chicken stock, cover tightly and roast in the oven until turkey reaches 70C when an instant-read thermometer is inserted into inner layer of meat, about 60 to 65 minutes.
9) Remove the turkey breast from oven and transfer to a cutting board to rest.
For the gravy:
1) Add apple cider, 125ml chicken stock, vinegar and remaining sage to the onions, chicken stock and juices in the roasting pan, bring to the boil and cook for approximately 10 minutes, stirring occasionally, until liquid is reduced by 1/3.
2) Slowly add the cornflour mixture, stirring constantly, and cook for 3 minutes more. The gravy should not be thick, just slightly thicker than a jus. Season with salt and pepper, to taste. Makes 375ml gravy.
Remove twine from turkey breast and slice into 3-cm thick pieces. Serve with gravy.