Creamy Cheesy Potato Au Gratin

Preheat the oven to 400°F (200°C). It's essential to preheat, as this will ensure the gratin cooks evenly.

While the oven heats, peels the potatoes and slice them into thin pieces, around 1/8 inch thickness. I find using a mandolin makes this task quicker and easier.

In a medium saucepan, heat the butter on medium flame. When the butter has melted, add the chopped onions and minced garlic, and cook until the onions are translucent. This step is what boosts the savory flavor profile of this dish.

Add the heavy cream to the pan and stir. When the cream is close to a boil, reduce the heat to low, add the potato slices, ensuring they are mostly submerged in the cream. This helps the potatoes to absorb the cream, enhancing its flavor and making it more tender.

Butter a casserole dish and transfer half of the cream-soaked potatoes into it. Spread evenly.

Sprinkle half of both the Gruyere and cheddar cheese on the potatoes. Season with salt, pepper, and half of the thyme if using. Repeat with the remaining potatoes, cheese, and seasoning. This layered approach aids in having cheese in every bite, creating a more satisfying dish.

Cover the dish with aluminum foil and bake for 30 minutes. Then, remove the foil and bake for another 20–30 minutes until the top is golden and crisp. There's an art to the perfect gratin: you want to achieve a delightful contrast between the creamy inside and crispy, cheesy crust.

Let it cool for a little while; it allows for easier serving and ensures you don’t burn your tongue, as the gratin stays hot for a while out of the oven.