Scalloped Potatoes with Leeks

Preheat oven to 350 degrees. Butter a 12-cup baking dish. Melt butter in a skillet over medium heat. Add leeks, and cook until translucent, 3-4 minutes. Arrange ⅓ of the potatoes in dish, slightly overlapping slices. Sprinkle with ¼ tsp salt, half of the nutmeg and pepper, followed by ½ of the leeks and 1 cup of the cheese. Repeat. Then top with remaining potatoes in a spiral. Sprinkle with remaining cheese. Combine cream and stock. Pour over cheese and potatoes. Cover with parchment paper and foil. (Can be refrigerated overnight) Bake for 30 minutes. Increase temperature to 425, uncover, and cook until top is golden brown and potatoes are tender, about 45 minutes. Let rest for 15-30 minutes before serving.