This rich potato gratin has been a standby in my kitchen for years, a dish I turn to when I want something comforting yet special. I first put this combination together one cold December evening when I had leftover cheese and a bag of potatoes on the counter; the result was so silky and indulgent that it quickly became the side everyone requested for holiday meals. The thin, even potato slices melt into a tender interior while the gruyère forms a nutty, golden crust on top, creating a contrast of creamy and browned textures that keeps me coming back. I remember the first time I made this for a family dinner—my father, who rarely raves about food, took a slow second helping and sighed contentedly. That memory has stuck with me; this dish feels like a warm, edible hug. It’s deceptively straightforward: a simple cheese sauce enriched with butter and a touch of nutmeg, layered with thinly sliced potatoes and finished with a generous scattering of gruyère. Use a mandoline for uniform slices, and you’ll get even cooking and the most pleasing mouthfeel.

Ingredients

• All-purpose flour: 3 tablespoons. If you need a gluten-free option, use certified gluten-free flour 1:1. The flour gently thickens the sauce; cook it briefly to remove the raw flour flavor.
• Whole milk or heavy cream: 1 1/2 cups. Whole milk yields a lighter, silkier sauce, while heavy cream makes the dish even richer and more indulgent—I often use a mix if I want balance.
• Gruyère cheese: 1/2 cup shredded for the sauce plus 1 cup shredded for layering and topping. Choose a good-quality gruyère or an aged Swiss for a nutty, savory character; freshly grate it for best melting.
• Nutmeg: A pinch. Freshly grated nutmeg brightens the dairy flavors—use sparingly so it complements but doesn’t dominate.
• Fresh thyme: 1 teaspoon chopped (or 1/2 teaspoon dried). Thyme lends an aromatic, slightly floral note that pairs beautifully with gruyère.
• Unsalted butter: 3 tablespoons. Use European-style butter if you want a richer flavor; it helps sweat the onion and build the base of the sauce.
• Small onion: 1, minced (about 1/4-inch pieces). A sweet onion or yellow onion works well—sweat it slowly to release sweetness without browning.
• Garlic: 1 clove, grated or minced. Adds a subtle backbone—don’t overdo it.
• Potatoes: 4 pounds, peeled and sliced thin (about 1/8-inch thickness). Starchy varieties like Russet or a mix of Yukon Gold and Russet work best for a tender interior and good structure.
• Salt and black pepper: To taste. Season each layer lightly; potatoes need seasoning through the dish, not just on top.

Instructions

Prepare the potatoes: Preheat the oven to 375°F. Peel the potatoes and slice them uniformly to about 1/8 inch using a mandoline or a very sharp knife; uniform thickness ensures even cooking. Place the slices in cold water for 10 minutes to remove excess surface starch, which helps prevent gluey layers—drain and pat dry thoroughly with clean kitchen towels before layering. Make the cheese sauce: In a medium saucepan, melt 3 tablespoons unsalted butter over medium heat. Add the minced onion and sweat gently for 5 to 7 minutes until translucent but not browned—this releases sweetness. Add the grated garlic and stir briefly, then sprinkle in 3 tablespoons flour and whisk continuously for 1 to 2 minutes to form a blond roux. Gradually whisk in 1 1/2 cups whole milk or cream, add 1 teaspoon fresh thyme and a pinch of ground nutmeg, and simmer gently until the mixture thickens enough to coat the back of a spoon, about 4 to 6 minutes. Remove from heat and stir in 1/2 cup shredded gruyère until melted; season carefully with salt and freshly ground black pepper. Assemble the layers: Butter a 9x13-inch baking dish. Arrange a single even layer of potato slices across the bottom, overlapping slightly. Lightly season with salt and pepper, spoon one third of the cheese sauce evenly across the potatoes, and scatter a portion of the shredded gruyère (about one-third of the 1 cup). Repeat two more times, finishing with the remaining cheese on top. Press down gently on the layers to remove air pockets and to settle the casserole so it bakes evenly. Bake until tender and golden: Cover the dish tightly with foil and bake at 375°F for 40 minutes. Remove the foil and continue baking for an additional 20 to 30 minutes until the top is bubbling and deeply golden. Test doneness by inserting a skewer into the center; the potatoes should be tender and glide off the skewer. Let the gratin rest 10 to 15 minutes before slicing to allow the sauce to set for neat portions.

Storage Tips

Store leftover gratin in an airtight container or covered tightly with foil in the refrigerator for up to 4 days. To reheat, cover with foil and warm in a 350°F oven until heated through, about 15 to 20 minutes, or reheat individual portions in the microwave, then crisp the top under the broiler for a minute if desired. For freezing, cool completely, wrap tightly with plastic wrap followed by foil, and freeze up to 3 months. Thaw overnight in the refrigerator before reheating; expect the top to brown less dramatically after freezing, so a quick broil can restore color.

Ingredient Substitutions

If you need to adapt the ingredients, swap whole milk for a 50/50 mix of milk and heavy cream to maintain richness while reducing total fat slightly. Use Gruyère for its nutty flavor, but Emmental or Comté are excellent alternatives; sharp cheddar will work but shifts the flavor profile. For a gluten-free option, substitute the all-purpose flour with a certified gluten-free 1:1 flour or use a cornstarch slurry (1 tablespoon cornstarch mixed with 2 tablespoons cold water) added at the end of the sauce cooking to thicken. For a lighter version, use Yukon Gold potatoes instead of Russet; they hold together better and provide a creamier mouthfeel.

Serving Suggestions

Serve the gratin as a luxurious side to roasted chicken, beef tenderloin, or a simple pan-seared salmon. Pair it with a crisp green salad dressed with lemon vinaigrette to cut through the richness, or add a bright vegetable like roasted asparagus or green beans with toasted almonds. Garnish with a few fresh thyme leaves or a sprinkle of flaky sea salt for a finishing touch. For a holiday spread, place the gratin center stage next to glazed ham and braised greens for a crowd-pleasing combination.

Cultural Background

This style of gratin draws inspiration from the classic French gratinée family, particularly gratin dauphinois from the Dauphiné region. Traditional preparations vary—some recipes use cream only, some include cheese in the layers, and others cook potatoes in milk with garlic rubbed on the dish. The technique of baking thinly sliced tubers in a creamy sauce dates back centuries in France, where hearty, slow-baked dishes were valued for feeding families through cold months. This modern take balances tradition and approachability, using gruyère for its characteristic flavor.

Seasonal Adaptations

Adjust the herb profile with the seasons: in spring and summer, fold in chopped chives or snipped basil at the end for brightness; in fall and winter, stick with thyme and a small pinch of freshly ground nutmeg. Swap half the potatoes for thinly sliced parsnips or sweet potatoes for a seasonal twist—parsnips add an earthy sweetness and hold their shape well. For holiday tables, stud the top with a handful of toasted walnuts or a dusting of smoked paprika to add visual interest and an extra flavor layer.

Meal Prep Tips

This is an excellent make-ahead option: prepare and assemble the casserole up to 24 hours in advance and keep it covered in the refrigerator. When ready to bake, let it sit at room temperature for about 30 minutes to take the chill off, then follow the baking times and check for tenderness. For workweek dinners, halve the recipe and bake in an 8x8-inch dish for quicker cooking; leftovers reheat beautifully for packed lunches and can be portioned into individual containers for grab-and-go meals.

Finally, I encourage you to make the dish your own: experiment with herbs, cheeses, and potato varieties until it sings for your family. There’s a comforting ritual in slicing the potatoes, building the layers, and waiting for the golden top to appear—which, for me, is one of the small joys of cooking and sharing food with loved ones.