For the stuffed pork, cut the pork in half, then cut a slit into the middle of each piece and stuff the sage leaves into the slits.
Place the flour onto a plate and coat the pork with the flour, shaking off any excess.
Melt the butter with the oil in a frying pan and fry the pork for 4-5 minutes on each side, or until completely cooked through. Leave the pork to rest in a warm place.
For the sauce, melt the butter in a frying pan and cook the onion, apple and sugar over a low heat for 4-5 minutes, or until softened.
Add the wine to the pan and simmer until reduced by half.
Add the double cream and mustard to the pan, season with salt and freshly ground black pepper and bring to a simmer. Remove from the heat and add the herbs to the sauce.
To serve, place the pork onto a plate and pour over the sauce.