Heat duck fat in a frying pan over medium heat, add onion and stir occasionally until lightly caramelised (5-10 minutes). Transfer to a large bowl and set aside until cool.
Lay the boned goose flat and skin-side down on a work surface. Carefully separate the meat from the skin with a sharp knife, being careful to keep the skin intact. Set skin aside in refrigerator, then remove sinew from flesh and discard. Dice breasts and transfer to bowl with cooled onion. Pass remaining goose meat, bacon, foie gras and duck livers through the coarse blade of a mincer into the bowl with the onion mixture (alternatively finely chop ingredients). Add breadcrumbs, egg yolks and sage, mix thoroughly using your hands, season to taste and set aside in the refrigerator until required.
Preheat oven to 200C. Lay goose skin on a work surface fat-side up and, using a scraping motion with a sharp knife (being careful not to break skin), clean the skin of all fat (discard). Squeeze excess water from caul, then lay in one large piece on a work surface. Place skin on top, skin-side down, then place mince mixture along the centre to form a log, leaving space at both ends. Fold caul and skin ends over stuffing, then roll away from you to completely enclose and form a tight log. Wrap log tightly in 4 layers of foil, twisting ends to seal, then place on a roasting tray and roast, turning occasionally, until cooked through (2 hours). Remove from oven and rest in foil for 30 minutes.
Meanwhile, for braised cabbage, heat duck fat in a large saucepan over medium heat, add cabbage and garlic, season to taste and stir occasionally until just tender (5-10 minutes). Keep warm.
For cinnamon apples, halve apples horizontally and remove core using a melon baller. Heat a frying pan over medium heat, add butter, cinnamon and apples, cut-side down, and cook until starting to soften (3-5 minutes). Add sugar and turn occasionally until caramelised (3-5 minutes). Keep warm.
Arrange cabbage on a serving platter. Carefully unwrap goose from foil and transfer to platter (you’ll have a lot of residual fat from the goose left in pan). Serve immediately with cinnamon apples.
Note Duck fat is available from select poultry shops and
delicatessens. Ask your butcher to bone the goose for you, leaving
it in one piece (you'll need to order it in advance). Foie gras is
available from fine food stores and select delicatessens. If
unavailable, substitute Cox with another cooking apple, such as
Granny Smith. Caul fat, also known as crépine, is the lace-like
fatty membrane that surrounds the intestines and stomach of cows,
sheep and pigs. It melts while it cooks, so is a useful alternative
to casing. Available from select butchers, it will need to be