For the paste filling, put rosemary,thyme, garlic, fennel seeds, chilli flakes, lemon zest, wine in a small food processor and blend until well combined.
Lay the pork (attached to the loin, butterflied, rind scored) out, skin-side down, and rub the paste over the pork, then roll it up as tightly as you can and secure at intervals with butcher’s twine.
If you have time leave in the fridge, uncovered or loosely wrapped in kitchen towel overnight – or even better, for two nights, to give the flavours time to permeate the meat and to let the skin dry out.
Arrange the potatoes and onion slices on the base of a large roasting tin and season with salt. Pour over the cider and stock (or water).
Make sure the rind of the pork is dry and season it with salt. Place on top of the potatoes and onions. Put in the oven. Set it to combi mode 80%, 120°C, 68°C core probe, fan speed to 50%.
Use golden touch function to crisp up the skin.