Preheat your oven to 350°F (175°C).
Carefully slice your Russet potatoes into thin, even rounds, about ⅛ to ¼ inch thick. Feel free to leave the skins on for extra fiber and rustic charm!
In a medium bowl or large measuring cup, combine the heavy cream, kosher salt, and ground black pepper. Give it a good whisk until everything is well mixed.
Lightly coat a large gratin or shallow baking dish with non-stick cooking spray. Arrange about a quarter of your sliced potatoes in a single layer at the bottom of the dish.
Sprinkle a quarter cup of the grated Parmesan cheese evenly over the potato layer. Then, pour about a quarter of your cream mixture over the cheese and potatoes.
Repeat steps 4 and 5 three more times, creating four beautiful layers. Make sure to finish with the remaining cream poured over the top, followed by the rest of the Parmesan cheese. Gently press down on the layers with your hand to ensure the potatoes are well-submerged in the cream.
Place your baking dish on a rimmed baking sheet (just in case of any happy overflows!). Bake uncovered for about 60 minutes, or until the topping is beautifully golden brown and the potatoes are fork-tender. If the cheese starts browning too quickly, loosely cover the dish with a piece of foil for the remaining bake time.