Preheat the oven to 350°F/180°C in a fan forced oven.
Mix the softened butter with garlic, thyme, sage, parsley, orange zest, lemon zest, orange/lemon juice, salt and pepper.
Stuff the cavity of the turkey with orange slices, lemon slices, onion and fresh herb sprigs.
Carefully separate the turkey skin from the turkey breast. Pat the turkey skin dry. Using your hands, spread the herb butter between the turkey breast and skin, and generously slather the outside of the turkey. Save a bit of the herb butter for basting later.
Loosely cover with foil and place turkey in the preheated oven.
Cook the turkey for 15 minutes per pound (or 30 minutes per kilogram). Remove the foil when the turkey is ⅔ of the way cooked, and baste with remaining butter while it finishes cooking. The turkey is cooked when internal temperature is 165°F/75°C in the deepest parts of the turkey.
When turkey is cooked, remove from oven, cover with foil and allow to rest for 20 minutes before serving.