Requires: kitchen string, tooth picks
Preheat the oven to 200°C conventional oven/ 180°C fan-forced (400° Fahrenheit/Gas 6). Line a baking tray with baking paper.
Cut the red onion in half. Finely chop ½ of the red onion. Set aside the remaining half. Heat the olive oil in a non-stick frying pan over medium heat. Add finely chopped red onion and cook, stirring, until the onion is soft (approximately 4 minutes). Set aside to cool.
Place the bread slices in a small bowl and pour the milk over to soak for a few minutes. Break up the sausage meat with your hands and add it to the bowl. Add the cooled onion and chopped sage. Use clean hands (or you may wish to use disposable gloves) to mix until the sausage filling is well combined.
Roughly chop the remaining red onion, carrot and celery.
Line a clean work surface with cling film (plastic wrap). Line 6 kitchen strings along the plastic wrap (each string approximately 30cm long). Arrange the pancetta in overlapping slices on top of the plastic wrap (and kitchen strings). Arrange the chicken fillet slices on top of the pancetta, overlapping slightly. Season the chicken with salt and pepper. Spoon the sausage mixture evenly over the breast fillet leaving a 2cm border around the edges. Use the plastic wrap to roll up the chicken tightly to enclose the sausage filling. Use kitchen string to tie the chicken at 5cm intervals. Secure the ends with tooth picks.
Transfer the chicken to the prepared baking tray on top of the vegetables. Pour the chicken stock over the Rotolo di pollo (rolled chicken). Roast for 20 minutes, then remove from the oven.
Turn the Rotolo di Pollo, pour the white wine over the chicken and baste with pan juices. Cook, for a further 20 minutes or until cooked through. Transfer chicken to a serving dish and set aside to rest for 10-15 minutes.
Meanwhile to make a gravy, place the pan juices and sherry into a small saucepan over medium heat. Reduce the cooking liquid until it reaches a thick and rich gravy consistency. Strain the gravy through a sieve into a gravy boat, using the back of the ladle to extract as much flavour as possible.
Serve the Rotolo di pollo (rolled chicken) with pork sausage and sage stuffing with gravy and Peas with onion, carrot and pancetta – buon appetito.