Before cooking the pork, remove the meat from the fridge and bring it to room temperature if necessary.
For the pork, preheat the oven to its highest temperature. Pat the pork loin dry with kitchen paper. Place the meat onto a roasting tray.
Roast the meat in the hot oven for 12-15 minutes, or until the skin begins to blister and the meat takes on some colour. Reduce the oven temperature to 170C/150 Fan/Gas 3 and continue to cook the meat for a further 1 hour, or until completely cooked through. (The pork is cooked through if the juices run clear if pierced in the thickest part with a skewer.)
Transfer the pork loin to a chopping board and remove the skin in one piece using a sharp knife. Wrap the pork tightly in aluminium foil and set aside to rest.
Increase the oven temperature to 190C/170 Fan/Gas 5.
While the meat rests, place the skin onto a baking tray and sprinkle all over with salt. Cook in the oven for 18-20 minutes, or until golden-brown and very crisp, then remove from the oven.
For the roast potatoes, pour enough rapeseed oil into a deep-sided roasting tray to reach 0.5cm/½in up the sides. Carefully transfer the tray to the oven to heat the oil - this should take 15-20 minutes.
Meanwhile, boil the potatoes in a pan of salted water for 12-15 minutes, until almost tender. Drain well, shaking the potatoes in the colander to roughen the edges.
Carefully add the potatoes to the hot oil, as quickly as is safe to do so. (CAUTION: It is important the potatoes are dry before they are added to the oil - if they are wet the hot oil will spit. Take great care not to burn yourself.) Roast the potatoes for 30-40 minutes, turning a couple of times until golden-brown all over.
For the Yorkshire puddings, divide the oil equally among the 12 holes of a muffin tin. Heat the oil in the oven for 15-20 minutes, until smoking hot.
Whisk the milk and eggs together into a large bowl until well combined. Gradually sprinkle in the flour, whisking after each addition, until the mixture forms a smooth batter with the consistency of double cream. Add the dried sage and onion salt and whisk again. Transfer the batter to a large jug, then set aside to rest for 5 minutes.
When the oil is very hot, carefully remove the muffin tin from the oven and pour enough batter into each of the wells to reach 1.5cm/½in up the sides. Return the muffin tin to the oven and cook the Yorkshire puddings for 18-20 minutes, or until risen, crisp and golden-brown.
Meanwhile, for the mash, boil the swede and carrots in a pan of salted, boiling water for 25-30 minutes, or until tender. Drain well and mash with the butter until smooth. Season, to taste, with salt and freshly ground black pepper.
Meanwhile, for the apple sauce, heat the butter in a lidded saucepan over a medium heat. When the butter is foaming, add the apple and a splash of cold water, then cover the pan with the lid. Reduce the heat to low and cook the apples for 12-15 minutes, or until completely tender. Just before serving, stir in the honey and salt. Beat the mixture until well combined but still retaining some texture.
For the spring greens, heat the oil in a large frying pan over a high heat. Add the chopped bacon and fry for 3-4 minutes, stirring regularly, until the fat has melted and the bacon is crisp and golden-brown.
Add the spring greens to the pan and stir-fry for 1-2 minutes, or until wilted and coated in the fat. Season, to taste, with salt and freshly ground black pepper, then stir in the hazelnut pieces.
To serve, slice the pork loin joint into 6 one-bone portions or cutlets. Serve the Yorkshire puddings, vegetables and apple sauce alongside.