Get the Baking Dish Ready: Preheat your oven to 350°F (175°C) to prepare for baking. Grease a 9x13-inch baking dish or a flan dish with softened butter, making sure to cover the sides and bottom.

Layer the Potatoes and Cheese : Arrange a single layer of the thinly sliced potatoes in the bottom of the prepared dish. Sprinkle a bit of the minced garlic and a handful of grated Gruyère cheese over the potatoes. Repeat the layers of potatoes, garlic, and Gruyère until all ingredients are used, finishing with a layer of cheese on top.

Prepare the Custard Mixture: In a medium bowl, whisk together the eggs, heavy cream, salt, black pepper, and grated nutmeg until well combined.

Assemble and Bake: Slowly pour the custard mixture over the layered potatoes, allowing it to soak into each layer. Gently press down on the potatoes to help the custard spread evenly. Shield the dish with aluminum foil and place it in the preheated oven for 45 minutes. Once the time is up, take off the foil and continue baking for another 15 to 20 minutes, or until the top achieves a lovely golden hue and the potatoes are tender.

Cool and Serve: Remove the flan from the oven and let it rest for 10 minutes before serving. This will help the flan set slightly, making it easier to cut and serve.