This lovely potato gratin is the perfect supper dish, so filling it needs little else served alongside. The gratin requires good waxy potatoes such as Charlotte or Maris Peer and bacon pieces plus a proper pouring of cream to create an unctuous sauce. For real success with this dish, you must use a strongly flavoured cheese like a Reblochon for the strong taste to stand out.
Preheat the oven to 150C and grease a 10 x 12-inch shallow baking dish with a little of the butter.
Peel and slice the potatoes into thick slices, approximately 1/8-inch thick. Place the potatoes in a colander and rinse thoroughly under cold, running water. Dry with kitchen paper and season well with salt and pepper (potatoes soak up a lot of salt while cooking, so be generous). Keep to one side.
Cut the cheese into small cubes.
Heat a large frying pan to hot but not burning. Dry fry (fry without any fat) for about 5 minutes until the bacon lardons are crisp and golden. Drain on kitchen paper. Place half the potatoes neatly into the dish, sprinkle over the bacon, then top with half the cheese followed by the remaining potatoes.
Pour in enough cream to just cover the potatoes—don’t worry if you don’t use it all. Dot the surface with the remaining butter.
Bake in the preheated oven until the potatoes are tender when pricked with a knife, about 1 1/4 hours.
Remove the baking dish from the oven, dot the surface with the remaining cheese and return to the oven and cook until bubbling and golden, about 15 minutes. Remove from the oven and leave to stand for 15 minutes covered in foil before serving.