Method

Heat the fan oven to 180C
Mix the onion, garlic, sausage, breadcrumbs and herbs in a large bowl, adding a generous amount of salt and pepper.
Flatten the boned leg meat with a mallet or rolling pin (skin side down with clingfilm cover) to about 1 cm thickness.
Spread the stuffing mixture over the leg then roll into a sausage shape. Tie the ends and at 3cm intervals with butchers twine.
Coat the leg with olive oil and oven cook in a meat pan for 15 minutes then drop the oven tempurature to fan 150C and continue cooking for about 20 minutes more.
Before the end of the planned cooking time check progress with a meat thermometer (70C) or for clear juices with a skewer. Cook until the meat is fully done.
Allow to rest, loosely covered with foil for at least 20 minutes.