The Glaze: Put the Guinness, honey and sugar into a pan, and reduce by almost half to form a sweet, syrupy glaze, then allow to cool.
Heat the oven to 200ºC/fan 180ºC/gas 6.
Season the pork with pepper and salt, if you want, place on a baking tray, and roast for 20 minutes. Then turn the heat down to 160ºC/fan 140ºC/gas 3. Remove the pork from the oven and brush all over with most of the glaze (save a few tablespoons), cook for a further 40-50 minutes, brushing and basting the pork as it cooks until it’s beautifully caramelised and glazed.
Remove the pork from the roasting tray and leave to rest.
Pour the remaining glaze into the roasting tray, then add the wine, Champagne or water. Place the pan on the heat and bring everything to the boil. Simmer for a few minutes until you have a thick gravy.
Carve the pork into thin slices, glaze with the Guinness syrup, drizzle a little on the plates and finish with a sprig of parsley.