Heat the olive oil in a frying pan and fry the pancetta over a medium heat for a few minutes. Stir in the garlic, add the sage and cook for a minute. Remove from the heat.
Slice each potato lengthways into thin slices. Place in a large bowl and add the pancetta and oil mixture and the cream. Season with sea salt and black pepper. Toss together.
Put into a baking dish ensuring that the potato, pancetta and sage are evenly distributed. Cover with foil and cook in the oven for 40 mins. About 20 mins before the end of cooking remove the foil so that the surface of the potatoes browns.
Sprinkle over a little Parmesan 5 minutes before the end.