Trim any fat and sinew from the fillets, toss in olive oil and sprinkle with salt and pepper. Panfry over moderate heat for about 15 minutes, turning frequently. Remove from the pan, cover loosely with foil and rest. Put the pan back on the heat and add plenty of peeled apple slices and a small handful of fresh sage leaves. Panfry, stirring frequently until the apple slices are well browned and tender. Turn up the heat, add a big splash of dry cider and let it bubble for a few minutes.
Taste, season and serve with the sliced pork fillet.