Creamy Potato Gratin Thyme

I was standing in a tiny kitchen in Lyon, watching my host's grandmother layer potatoes into a worn ceramic dish with the kind of ease that comes from fifty years of Sunday dinners. She didn't measure anything, just poured cream until it looked right and tossed in thyme she'd clipped that morning. That gratin, golden and fragrant, taught me more about French cooking than any cookbook ever could.

The first time I made this for friends, I panicked because the cream looked like too much, but I trusted the recipe and watched it disappear into the potatoes as they baked. When I pulled the dish out, bubbling and bronze at the edges, someone actually gasped. We ate it straight from the pan with a bowl of bitter greens, and no one spoke for the first five minutes.

Ingredients

• Yukon Gold or Russet potatoes: Yukon Golds give you a buttery texture and hold their shape beautifully, while Russets break down slightly for extra creaminess. Slice them as thin and even as possible so they cook through at the same rate.
• Heavy cream and whole milk: This combination keeps the sauce rich without being overwhelming. I learned the hard way that low-fat milk makes the sauce split and taste thin.
• Gruyère cheese: It melts like a dream and has a nutty, slightly sweet flavor that defines a proper gratin. If you can't find it, Emmental or a good sharp white cheddar works in a pinch.
• Parmesan cheese: Adds a salty, umami depth that balances the cream. Freshly grated is always better than the pre-shredded stuff, which can taste dusty.
• Fresh thyme: The leaves release their fragrance as the gratin bakes, filling your kitchen with an herbal warmth that dried thyme just can't match.
• Garlic and nutmeg: Garlic brings a mellow sweetness when warmed gently, and nutmeg adds a mysterious, cozy note that people notice but can't quite name.
• Unsalted butter: Greasing the dish and dotting the top ensures those crispy, golden edges that everyone fights over.

Instructions

Prep your dish and oven:

Preheat your oven to 180°C (350°F) and generously butter a 2-liter baking dish, making sure to get into the corners. This prevents sticking and adds a hint of richness to the edges.

Warm the cream mixture:

Combine the cream, milk, garlic, nutmeg, salt, pepper, and thyme leaves in a saucepan over medium heat, stirring occasionally until it just begins to steam. Don't let it boil or the cream can break and turn grainy.

Build the first layer:

Arrange half the potato slices in overlapping rows, like shingles on a roof, then scatter over half the onions, Gruyère, and Parmesan. Pour half the warm cream mixture evenly over the top, letting it seep between the slices.

Add the second layer:

Repeat with the remaining potatoes, onions, and cheeses, then pour over the rest of the cream. Press down gently with your hands to compact the layers and make sure everything is submerged.

Top and cover:

Dot the surface with small pieces of butter, sprinkle on extra Gruyère and a few thyme leaves, then cover tightly with foil. This traps steam so the potatoes cook through before the top browns.

Bake covered, then uncovered:

Bake for 40 minutes with the foil on, then remove it and bake another 20 minutes until the top is golden and bubbling at the edges. The smell will be intoxicating.

Rest before serving:

Let the gratin sit for 10 minutes so the layers set and the cream thickens slightly. Garnish with fresh thyme leaves and serve warm.

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One winter, I brought this to a potluck and watched a quiet, picky eater go back for thirds. She told me later it reminded her of her grandmother's cooking, even though her grandmother was Italian and never made gratin. Sometimes a dish just speaks to people in ways you can't predict.

How to Slice Potatoes for Gratin

A mandoline is your best friend here, set to about 2–3 mm. If you're using a knife, keep your fingers curled and take your time. The slices should be thin enough to see light through but thick enough to hold their shape. I like to slice them all first and keep them in a bowl of cold water if I'm not layering right away, then pat them dry before building the gratin.

Make-Ahead and Storage Tips

You can assemble the whole dish up to a day ahead, cover it tightly, and refrigerate. Just add an extra 10 minutes to the covered baking time since it'll be cold. Leftovers keep for up to three days in the fridge and reheat beautifully in a low oven, though the top won't be quite as crispy. I've even frozen individual portions wrapped in foil, then baked them from frozen for an easy weeknight side.

Serving Suggestions and Variations

This gratin shines next to roast chicken, beef tenderloin, or a simple pan-seared pork chop. For a lighter meal, I'll serve it with a bitter green salad dressed in lemon and olive oil. If you want to experiment, try swapping half the potatoes for thinly sliced sweet potatoes, or add a layer of sautéed mushrooms and leeks between the potato layers for an earthy twist.

• Add a pinch of cayenne to the cream mixture if you like a subtle kick of heat.
• Try Emmental or sharp cheddar if Gruyère isn't available.
• For a gluten-free version, just double-check your cheese labels.

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There's something about pulling a gratin from the oven, all golden and bubbling, that makes you feel like you've really cooked. I hope this one becomes a favorite in your kitchen, too.

Recipe Questions

→ What type of potatoes work best for this dish?

Yukon Gold or Russet potatoes are ideal due to their firm texture and ability to hold shape when thinly sliced and baked.

→ Can I substitute the cheeses in the gratin?

Gruyère can be replaced with Emmental or sharp cheddar, which still melt well and provide a rich flavor.

→ How do I ensure the gratin is creamy without being watery?

Gently heating the cream with garlic, nutmeg, and thyme before layering helps infuse flavor without excess liquid, and baking uncovered at the end allows evaporation for a perfect texture.

→ Is fresh thyme necessary or can dried thyme be used?

Fresh thyme provides brighter aroma and flavor, but dried thyme can be substituted if fresh is unavailable, using half the amount.

→ What is the best way to slice the potatoes evenly?

Using a mandoline or a sharp knife ensures uniform thin slices (2-3 mm), promoting even cooking and texture.

→ Can this dish accommodate a gluten-free diet?

Yes, ensure that the cheeses used are certified gluten-free to keep the dish suitable for gluten-sensitive diets.