Preheat oven to 180ºC. Lightly grease an ovenproof dish with butter - use a deep large dish about 30 x 30 cm.
Thinly slice the potatoes. Arrange some of the potato over the base of the ovenproof dish. Season with salt and cracked black pepper. Continue layering with the remaining potato and seasoning between the layers.
Combine cream with 3 tablespoons of cheese and add a handful of fresh thyme (optional). Pour in the combined cream and cheese as you add potato layers or pour it all in at the end of layering. Sprinkle one tablespoon of parmesan on top, then cover with oiled foil.
Bake for 45 to 50 minutes or until the potato is cooked through and the top is golden. In the interim fry chopped bacon in some olive oil until crispy. When the gratin is cooked remove the foil and spoon on the bacon pieces. Put back in the oven for ten minutes until the top is golden. Stand for 5 minutes before serving.