Remove the foil and continue baking uncovered for another 15 to 20 minutes, until the potatoes are completely tender all the way through and the cheese around the edges of each cup has turned deeply golden and beautifully crisp. Keep a watchful eye on them during the final stretch, as ovens vary and you want golden perfection rather than anything burnt.
Allow the potato stacks to rest in the pan for about five minutes after pulling them from the oven. Then run a small knife carefully around the edge of each cup to loosen the stacks, and lift them out gently using a spoon or a small offset spatula. Arrange them on a serving platter and bring them to the table immediately.
Serve the cheesy potato stacks while they are still hot, while those edges are at their crispiest and the cheese in the center is beautifully melted and gooey. Any stacks that cool down can be brought back to life by rewarming them in a 350-degree oven for five to ten minutes to restore their wonderful texture.
