Make a brine with 20gm fine sea salt and 500ml water and brush it over the skin of the pig (do not get brine on the meat). Break down the pig into sub-primal cuts - belly, rack, loin, leg, shoulder, and neck (reserving bones for sauce; see note). Remove the offal - kidney, cheek, ear, tongue, snout, and tail. Refrigerate everything until required.
For pork sauce, preheat oven to 180C, and cut bones and trotters up (set a quarter of the bones aside to add to the stock later to freshen) and coat in 1 tbsp olive oil, season to taste and roast in a roasting pan until golden (40-50 minutes). Transfer to a large saucepan, cover completely with stock, then simmer over medium heat until stock is well flavoured (1-1½ hours). Strain, discard bones and reserve stock. Meanwhile, boil Port, cinnamon and star anise in a large saucepan over high heat until reduced by half (30-40 minutes). Add onion, carrot, celery and garlic, stir to combine, then add reserved pork stock and cook over low-medium heat until reduced to a sauce consistency (2 hours; adding ginger, sage and remaining pork bones during last 30 minutes of cooking). Strain through a fine sieve. Makes 500ml.
Preheat oven to 150C. Place shoulder on an oven tray lined with baking paper, rub 2 tsp olive oil on the skin side, season to taste and roast until very tender (3 hours). Combine 100ml pork sauce with offal, ginger and the chopped sage in a casserole, cover and braise in oven until tender (3 hours). Strain off liquor and set aside.
For caramelised apples, heat 2 large heavy-based frying pans over medium heat, add sugar, butter and apples and cook until just starting to caramelise (2-3 minutes). Keep warm.
Increase oven to 220C. Melt butter with garlic and set aside. Add 5mm oil to 2 frying pans over medium-high heat and sear the pork cuts, in batches of cuts, skin-side down to crisp up the crackling until golden and crunchy (3-4 minutes), then transfer to an oven rack and roast until internal temperature is 55C (5-10 minutes). Take the meat out of the oven and baste with butter mixture, then set aside to rest (10 minutes).
Meanwhile, for celeriac rémoulade, combine ingredients in a bowl, season to taste and set aside.
For bitter leaf and apple salad, combine ingredients in a bowl, toss and set aside.
Place a small heaped pile of celeriac rémoulade and half a caramelised apple on each serving plate. Slice a piece of each cut of meat 1cm thick and arrange on each plate, top with salad and finish with pork sauce drizzled around.