Scalloped Potatoes with Gruyère and Thyme
Creamy, tender potato slices baked with nutty Gruyère cheese and fresh thyme. This classic French-inspired gratin features a rich sauce that transforms into a silky custard as it bakes, with a golden, lightly crisped top. Perfect as an elegant side dish or standalone comfort food.
Steps
Before you start
- Preheat your oven to 375°F (190°C)
- Use a sharp mandoline or knife to slice potatoes uniformly—thin, even slices cook evenly and layer beautifully
- Have all ingredients measured and ready before you begin layering
Prepare the cream sauce
- In a large mixing bowl, combine the 2 cups (480 ml) heavy cream, 1 cup (240 ml) whole milk, minced garlic, 4 fresh thyme sprigs, 1 teaspoon (6 g) kosher salt, ½ teaspoon (1 g) black pepper, and ¼ teaspoon (0.5 g) freshly grated nutmeg.
- Whisk until well combined.
- Let the mixture infuse for 5 minutes so the thyme and garlic flavor the cream.
- Remove the thyme sprigs.
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Ready when: Thyme sprigs have released their oils; mixture is fragrant and well-flavored
Tip: Don't skip the infusion time—it's where the sauce gets its delicate herbal depth.
Prepare the baking dishOven 375°F / 190°C
- Preheat your oven to 375°F (190°C) if you haven't already.
- Lightly butter a 9×13-inch (23×33 cm) baking dish, coating the bottom and sides to prevent sticking.
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Tip: A lightly buttered dish prevents sticking but doesn't need a thick coating—just enough to coat.
Layer potatoes and cheese
- Spread about 1 cup (284 g) of the sliced potatoes in an even layer on the bottom of the prepared baking dish.
- Sprinkle with about ¼ teaspoon of the stripped thyme leaves and about 3 tablespoons (21 g) of the grated Gruyère.
- Repeat this layering, alternating potatoes, thyme, and cheese, until all potatoes and cheese are used, ending with a final thin layer of potatoes on top (reserve about 2 tablespoons of cheese for the top).
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Ready when: All potatoes and cheese are layered; the dish is full but not overflowing
Tip: Keep potato slices as uniform as possible so they cook evenly—a mandoline slicer is your best friend here.
Pour cream sauce
- Carefully pour the infused cream mixture over the layered potatoes, allowing it to settle between the layers.
- Pour slowly so the cream flows down throughout the stack rather than pooling at the edges.
- The cream should reach about three-quarters of the way up the potatoes; don't overfill or it will bubble over in the oven.
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Ready when: Cream is distributed throughout the layers; the top layer of potatoes is just covered or barely visible
Tip: If you pour too quickly, the cream runs off to the edges and misses the middle layers—slow and steady wins here.
Top with cheese and butter
- Sprinkle the reserved 2 tablespoons (14 g) of grated Gruyère evenly over the top layer of potatoes.
- Distribute the 3 tablespoons (43 g) cold butter cubes evenly across the surface—these will melt and create a golden, crispy top.
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Ready when: Cheese and butter are evenly distributed across the top
Tip: Cold butter creates a more flavorful, golden crust than melted butter—resist the urge to melt it first.
Bake until golden and tenderOven 375°F / 190°C
- Place the gratin in the preheated 375°F (190°C) oven on the middle rack.
- Bake for 45–50 minutes, until the potatoes are completely tender when pierced with a fork and the top is golden brown with a few darker, caramelized patches.
- If the top begins to brown too quickly (after about 30 minutes), cover loosely with foil and continue baking until the potatoes are fork-tender.
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Ready when: Potatoes are completely tender when pierced with a fork; top is golden brown with some caramelized edges; cream has thickened and is mostly absorbed
Tip: Don't open the oven door repeatedly—each peek lowers the temperature and extends cooking time. If the top is browning too fast, use foil to gently shield it.
Rest before serving
- Remove the gratin from the oven and let it rest on the countertop for 10 minutes.
- This allows the cream to set slightly and makes the dish easier to portion without falling apart.
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Ready when: Gratin is still warm to the touch; slight jiggle in the center is normal
Tip: These 10 minutes are essential—diving in immediately can result in a runny, soupy mess. Patient cooks are rewarded with perfect slices.
Good to know
Tips
- Uniform potato slicing is non-negotiable—use a mandoline on its thinnest setting (⅛ inch / 3 mm). Unevenly sliced potatoes create some mushy and some raw pieces.
- The cream-to-potato ratio is calibrated for a 9×13-inch dish; if you use a different-sized dish, the liquid depth changes. Adjust the cream amount so it reaches about three-quarters of the way up the potatoes.
- Infusing the cream with thyme and garlic is the secret to restaurant-quality flavor—don't skip it or add raw garlic directly to the layers, which can be harsh.
- Let the gratin rest after baking; this is when the residual heat finishes cooking any undercooked spots and the sauce sets enough to slice cleanly.
Make ahead
Assemble the gratin through Step 4 (potatoes and cream in the baking dish, but not yet topped with cheese and butter) up to 8 hours ahead. Cover tightly with plastic wrap and refrigerate. Add the cheese and butter topping just before baking, and increase the baking time by 5–10 minutes since it will start cold.
Storage & reheating
Store leftovers in an airtight container in the refrigerator for up to 3 days. To reheat, cover loosely with foil and warm in a 325°F (163°C) oven for 15–20 minutes until heated through. Do not freeze, as the cream-based sauce becomes grainy when thawed. Leftovers are also delicious at room temperature as a side salad.
Substitutions
- Gruyère cheese, aged 6 months or more → Emmental or aged Comté cheese. Both have similar nutty, complex flavors and melt beautifully. Use the same weight. Avoid young, mild Gruyère, which lacks depth.
- heavy cream → Half-and-half mixed with whole milk (1 cup half-and-half + 1 cup whole milk). Creates a slightly lighter sauce with less richness but still creamy. The custard will be less unctuous.
- fresh thyme sprigs → Fresh rosemary or a combination of thyme and sage. Both are classic gratin herbs. Use sparingly with rosemary (it's assertive) and only the tender leaf tips.
- Yukon Gold potatoes → Russet or red potatoes. Russets are starchy and will create a thicker sauce; reds stay firmer but are slightly less creamy. Both work, though Yukon Golds remain ideal for their balance.
