1. Preheat your oven to 375°F (190°C). Butter a 9×13-inch baking dish generously to prevent sticking and add richness to the edges.
2. Wash, peel, and slice the Yukon Gold potatoes into thin, even slices—about 1/8 inch thick. I find a mandoline slicer makes this step much easier and safer, but if you don’t have one, a sharp knife works just fine. When I first started making this gratin, I remember how nervous I was about slicing evenly, but it gets easier with practice!
3. In a medium saucepan, combine the heavy cream, whole milk, minced garlic, thyme, rosemary, salt, and pepper. Warm over medium heat until just simmering, then remove from heat. This infuses the cream with herbal goodness, which is key to that deep flavor I love.
4. Arrange a layer of potato slices evenly on the bottom of the prepared baking dish. Pour a ladleful of the warm cream mixture over the potatoes, then sprinkle a generous handful of Gruyère and a light dusting of Parmesan on top.
5. Repeat the layering process—potatoes, cream, cheese—until you run out of ingredients, finishing with a final layer of cheese on top. This layering method is something I learned from my grandmother; it creates that perfect balance of creamy, cheesy, and tender potatoes.
6. Cover the dish tightly with aluminum foil and bake for 45 minutes. Then, remove the foil and bake for an additional 25-30 minutes, or until the top is golden brown and bubbling, and the potatoes are tender when pierced with a fork.
7. Let the gratin rest for 10-15 minutes before serving. This step is crucial—it allows the layers to set and makes slicing easier. Plus, it gives you a moment to breathe and appreciate the beautiful aroma filling your kitchen.

Pro tip: If you’re like me and love that golden, slightly crispy top, you can switch your oven to broil for the last 2-3 minutes—just watch closely so it doesn’t burn!