Fry onion, garlic, and green pepper in oil for two minutes.
Add sherry and wine, then reduce liquid by two-thirds and cool.
Mix cooled onion mixture with sausage meat, sweetcorn, and parsley.
Prepare turkey by removing wishbone and breaking the back bone.
Fill neck cavity with stuffing and secure with string or a skewer.
Preheat oven to 220°C.
Baste turkey with butter and roast on one side for 30 minutes.
Turn turkey over, baste with juices, and roast at 180°C for 30 minutes.
Turn turkey breast-side up.
Heat maple syrup and lemon juice to create a glaze.
Brush turkey with glaze and roast for approximately four hours.
Rest the cooked turkey for 15 minutes before carving.
Cook chopped onion in roasting tray until golden-brown.
Add wine and stock to tray and simmer to create gravy.
Thicken gravy with potato flour if desired, then strain and serve.