2) In a 23cm square casserole dish, arrange the potatoes in an even layer, one-slice thick. Drizzle with 3 tbsp of the cream mixture and season with salt and pepper. Repeat with the remaining potatoes, cream, salt and pepper to form 10 layers.
3) Cover and bake for 30 minutes. Remove the cover and continue baking for 45 minutes to 1 hour, or until the cream has been absorbed, the potatoes are cooked through and the top is browned.
4) If cooking from frozen, bake for 45 minutes and then allow to cool completely. Divide into portions and transfer to a freezer-safe container to cook from frozen later. When cooking from frozen, place the gratin into a baking dish and bake in a preheated oven at 160°C until tender and golden, about 30-35 minutes.