Trim the pork loin and keep trimmings
Make an incision along the side to create a pocket
Rub the pork with salt and pepper
Put the pork trimmings in a processor with chopped sage and egg white and puree well, add the leek and salt and pepper, plus a little nutmeg, stuff this inside the pork loin and tie up, stab with a knife an insert sage leaves in the incisions
Place into a roasting tray and drizzle with oil.
Roast in an oven at 375 till cooked approx. 1.5 hours
Take out and rest the pork
Add the chopped onion to a pan with a little butter, cook for 5 minutes.
Add a little sage and the Guinness and reduce, add a splash of red wine and the stock
Reduce and then thicken with the gravy mix, season with salt and pepper
Slice and serve topped with Guiness reduction.