Creating Potatoes Au Gratin is straightforward if you follow these easy steps:

1. Preheat Oven: Preheat your oven to 375°F (190°C). Prepare a baking dish by greasing it with butter.

2. Prepare Potatoes: Thoroughly wash and peel the russet potatoes. Using a mandoline or sharp knife, slice them into thin rounds (about 1/8-inch thick).

3. Mix Cream and Seasoning: In a mixing bowl, combine the heavy cream, minced garlic, salt, pepper, and thyme. Stir well to incorporate flavors.

4. Layer Potatoes: Arrange a layer of potato slices at the bottom of the greased baking dish. Slightly overlap each slice for even coverage.

5. Add Cheese: Sprinkle a handful of Gruyère cheese and Parmesan cheese over the first layer of potatoes.

6. Repeat Layers: Continue the layering process by adding more potato slices, followed by the cream mixture and cheese. Repeat until all ingredients are used, finishing with a layer of cheese on top.

7. Cover and Bake: Cover the baking dish with aluminum foil to prevent burning. Bake in the preheated oven for 30 minutes.

8. Uncover and Brown: After 30 minutes, remove the foil and continue to bake for an additional 10-15 minutes, or until the top is golden brown and bubbly.

9. Cool Slightly: Once done, take it out of the oven and allow it to cool for about 10 minutes before serving.

This step-by-step approach ensures incredibly delicious Potatoes Au Gratin, with each layer contributing to the overall richness.