Preheat the oven to 200ºC/400°F/gas 6.To remove the pork skin, slice around the edge of the skin (in the middle of the fat), then continue slicing and pulling back the skin until you can remove it in one piece.Place the skin skin-side up and carefully score all over at 1cm intervals (I like to use a Stanley knife). Flip over and score the fat in a criss-cross pattern to help it render quickly. Lightly score the fat of the pork joint, also at 1cm intervals, almost down to the meat.Put the fennel seeds into a pestle and mortar, along with 2 teaspoons each of sea salt and black pepper. Finely grate in ½ a nutmeg, then bash until fine. Rub the spice mix all over the pork joint and skin, getting it right into the little grooves.Drizzle 1 tablespoon of olive oil in a casserole pan on a medium heat, add the pork, fat-side down and let the pork fat render as the pan heats up – around 5 minutes, basting occasionally (I like to use the bunch of sage to do this).Halve or quarter the fennel bulbs (reserving a few herby fennel tops for garnish later), trim the spring onions, and halve the garlic bulb then place in a large roasting tray with the bunch of sage.Place the pork joint into the tray fat-side up and roast at the bottom of the oven for 1 hour. Dip the pork skin into the rendered fat from the pan, and place directly on the bars of the oven, above the tray, so the fat rains down and bastes the joint as it cooks.For the gratin, chop the fennel (tops and all) into 1cm chunks, peel and chop the onion (or trim, if using spring onions), and peel and finely slice the garlic, then add to the pork fat pan on a medium heat and cook for 15 minutes, or until softened, stirring regularly.Season with a pinch of salt and pepper, then pour in the cider, turn the heat up to high and allow it to bubble and cook away.Add the anchovies and a drizzle of the oil from the tin (if using) and stir well for a minute or two, then stir in the chickpeas and both jars of beans (juices and all). Bring to the boil, add the crème fraîche and finely grate in most of the Parmesan, then mix together well. Finely grate over the remaining Parmesan, and switch off the heat.After 1 hour, remove the pork and crackling from the oven and leave to rest while you bake the gratin for 30 minutes, or until golden and bubbling.Toss the veggies from the pork tray in the meat juices and return to the oven for 5 to 10 minutes, or until golden and caramelised, then remove.When the pork has rested, it’s time to carve – slice down confidently between the ribs (for generous portions), or remove the ribs and slice the meat into nice thin slices (this will give you more portions). Clank up the crackling and arrange everything on a platter.Spoon the gratin onto serving plates, and top with the pork, caramelised veg (squeeze some of the garlic out of its skin and toss through first, if you like) and crackling. Drizzle over any resting juices, and scatter over the reserved herby fennel tops, to finish.