Preheat oven to 350 degrees. Bring a pot of water to a boil, add small amount of salt, and cook potatoes for 3 minutes, until slightly softened, then drain.
Bring more water to a boil, then blanch the leeks by boiling them for 1 minute, until softened, then drain.
Place half of the potatoes into a shallow baking dish and spread them out to the edge. Cover with two-thirds of the leeks, then add the remaining potatoes. Tuck the slices of cheese and the remaining leeks in amoung the layer of potatoes. Season with salt and pepper, and pour the cream over it all.
Bake for 1 hour, until tender and golden. Cover with foil if the top starts to over-brown before the potatoes are tender.