Preheat your oven to 375°F (190°C) and grease a 9x13-inch baking dish with 2 tablespoons of unsalted butter.

Thinly slice 3 pounds of peeled russet potatoes into even rounds, about 1/8 inch thick.

In a mixing bowl, combine 1 cup of heavy cream, 1/2 cup of shredded white cheddar cheese, 4 tablespoons of grated Parmesan cheese, and 3 minced garlic cloves. Stir well.

Add the sliced potatoes to the cream mixture and gently toss to coat. Season generously with salt and pepper.

Arrange the potato slices upright in the greased baking dish and pour any remaining cream mixture over the layers.

Cover the dish with aluminum foil and bake for about 35 to 40 minutes, or until the potatoes are fork-tender.

Remove the foil and sprinkle the remaining 2 tablespoons of Parmesan cheese over the top. Bake uncovered for an additional 25 to 30 minutes.

Switch to broil and place the dish under the broiler for about 1 minute for a crispy top. Let cool for 10 minutes before serving.