Potato gratin is a simple but impressive side dish: thinly sliced potatoes bake slowly in seasoned cream until tender, silky, and golden on top. The key is controlling slice thickness, moisture, seasoning, and oven temperature so the potatoes cook evenly without a watery sauce.
Ingredients
Serves 6 to 8 as a side dish.
- 2 pounds (900 g) Yukon Gold or other yellow-fleshed potatoes
- 1 1/2 cups (360 ml) heavy cream
- 1 cup (240 ml) whole milk
- 2 garlic cloves, finely grated or minced
- 1 1/2 teaspoons kosher salt, plus more for the dish
- 1/2 teaspoon freshly ground black pepper
- 1/4 teaspoon freshly grated nutmeg, optional
- 1 tablespoon unsalted butter, softened
- 1 cup (100 g) grated Gruyère, Comté, sharp Cheddar, or a mixture
- 2 tablespoons finely grated Parmesan, optional
- 1 tablespoon chopped fresh thyme, or 1 teaspoon dried thyme
Yukon Gold potatoes are especially useful because they have enough starch to help thicken the cream while still holding their shape. Russet potatoes also work and produce a softer, starchier gratin. Avoid very waxy potatoes if you want the sauce to become naturally thick and cohesive.
Equipment and preparation
Use a shallow 2-quart baking dish, approximately 9 by 13 inches or a similar size. A shallow dish gives the potatoes more surface area, helping the center cook before the top becomes too dark. A mandoline makes uniform slices quickly, but a sharp chef’s knife works well if you take care to keep the slices even.
- Heat the oven to 375°F (190°C). Place a rack in the middle position.
- Rub the inside of the baking dish thoroughly with the softened butter. Rub the cut garlic clove over the dish first if you want a stronger garlic flavor.
- Peel the potatoes if you prefer a completely smooth texture. Leaving the skins on is fine for thin-skinned potatoes, but scrub them well.
- Slice the potatoes 1/8 inch (3 mm) thick. Do not rinse the slices; the surface starch helps the cream thicken.
- Grate the cheese and measure the remaining ingredients before assembling. Once sliced, the potatoes should be layered promptly so they do not discolor.
Uniformity matters more than exact thickness. If some slices are paper-thin and others are nearly 1/4 inch thick, the thin slices may collapse while the thick ones remain firm.
Make the seasoned cream
Combine the heavy cream, milk, garlic, salt, pepper, nutmeg, and thyme in a saucepan. Warm the mixture over medium heat until steaming and just beginning to form small bubbles around the edges. Do not bring it to a vigorous boil. Heating the dairy first reduces the temperature drop when it goes into the baking dish and helps the gratin cook more evenly.
Taste a small spoonful of the warm mixture, allowing it to cool briefly first. It should taste slightly more seasoned than you want the finished sauce to taste because the potatoes will absorb some of the salt. If using a salty cheese such as Parmesan or aged Cheddar, keep the initial seasoning moderate.
You do not need to thicken the cream with flour. The potato starch released during baking should provide body. A flour-based sauce can be useful if you want an especially firm casserole, but it changes the texture from a classic cream-based gratin and can become pasty if overcooked.
Assemble the potato gratin
Arrange one layer of potato slices in the buttered dish, overlapping them slightly like shingles. Sprinkle with a little cheese, then add another layer of potatoes. Continue layering until all the potatoes are used, seasoning lightly between layers if needed. Finish with a neat layer of potato slices on top.
Pour the warm cream mixture slowly over the potatoes. Gently press the layers down with the back of a spoon so the liquid reaches the lower slices. The cream should come close to the top of the potatoes without completely submerging them. Sprinkle the remaining cheese over the surface.
A useful guide for the main proportions is below:
| Ingredient | Amount | Purpose |
|---|---|---|
| Potatoes | 2 lb / 900 g | Main structure and natural starch |
| Heavy cream | 1 1/2 cups | Richness and silky texture |
| Whole milk | 1 cup | Loosens the sauce without making it too heavy |
| Grated cheese | 1 cup | Savory flavor and browned topping |
| Salt | 1 1/2 tsp, adjusted | Seasons the potatoes and dairy |
Avoid packing the slices too tightly. They should overlap, but there must still be room for the cream to move between them. An overly compressed dish can take longer to cook and may develop firm, under-seasoned centers.
Bake until tender and golden
Bake the gratin uncovered for 55 to 75 minutes, depending on the depth of the dish and the thickness of the slices. Start checking at 50 minutes. The top should be deeply golden in spots, and a thin knife should slide through the center with little resistance.
If the cheese is browning too quickly while the potatoes are still firm, cover the dish loosely with aluminum foil. Continue baking until tender, then remove the foil for the final 10 to 15 minutes. If the top remains pale once the potatoes are cooked, move the dish to a higher oven rack for a few minutes or use the broiler briefly. Watch closely because cheese can burn quickly.
When the gratin comes out of the oven, rest it for 15 to 20 minutes before serving. The cream will continue to thicken, the layers will settle, and the slices will be easier to cut. Serving immediately is possible, but the sauce will be looser and more likely to run onto the plate.
Flavor variations and substitutions
A classic gratin needs only potatoes, dairy, seasoning, and perhaps cheese, but small changes can suit the rest of the meal.
- Extra-garlic gratin: Add another grated garlic clove to the cream and rub the baking dish with a cut clove.
- Herb version: Use thyme, rosemary, sage, or a small amount of chopped parsley. Add delicate herbs after baking so they stay fresh.
- Cheddar and onion: Add very thinly sliced, softened onions between the layers and use sharp Cheddar instead of Gruyère.
- Blue cheese: Replace up to one-third of the Gruyère with crumbled blue cheese. More can overpower the potatoes.
- No cheese: Omit the cheese for a simpler French-style cream gratin. Add a little extra black pepper and nutmeg for depth.
- Half-and-half: Substitute half-and-half for the heavy cream, but expect a lighter and slightly less luxurious sauce.
- Evaporated milk: Use it in place of the milk for a creamy result with less fat. Do not use sweetened condensed milk.
- Dairy-free: Use unsweetened, unflavored oat cream or a cooking cream designed for heat. Choose a neutral product; strongly flavored plant milks can make the dish taste sweet.
Be cautious with watery additions such as fresh tomatoes, zucchini, or large amounts of spinach. They release liquid and can prevent the cream from thickening. If adding vegetables, cook them first and drain them thoroughly.
Troubleshooting
The potatoes are still hard. The slices may be too thick, the dish may be too deep, or the oven may run cool. Cover the gratin with foil and continue baking in 10-minute intervals. Test the center rather than the edges, which cook faster.
The sauce is watery. The gratin may need more time, especially if the potatoes released water or the dish was covered for most of the bake. Return it to the oven uncovered until bubbling and thickened. Resting also makes a major difference. Next time, avoid rinsing the slices and use a shallower dish.
The top is burned. Cover the dish loosely with foil and lower the rack or reduce the oven temperature by 25°F (15°C). If the cheese is already too dark, scrape away only the bitter areas after resting and serve with a fresh garnish of herbs.
The gratin is bland. Potatoes absorb considerable seasoning. Salt the cream carefully after tasting it, and season lightly between layers. A flavorful aged cheese, garlic, black pepper, and nutmeg can add complexity without making the dish salty.
The cream curdled. Very high heat, low-fat dairy, or acidic ingredients can cause separation. Use full-fat dairy, avoid boiling the cream aggressively, and keep acidic ingredients out of the baking mixture. A slight separation is not dangerous, although the texture will be less smooth.
The slices are unevenly cooked. Slice more uniformly and arrange the thickest pieces toward the outside or lower layers. A mandoline is helpful, but always use its hand guard and keep your fingers away from the blade.
Make-ahead, storage, and reheating
You can assemble the gratin several hours ahead and refrigerate it covered. Let it sit at room temperature for about 20 to 30 minutes before baking, then expect the cooking time to increase slightly because the dish is cold. Do not leave raw potatoes submerged in cream at room temperature for extended periods.
For the best make-ahead result, bake the gratin until the potatoes are just tender but the top is only lightly colored. Cool it, cover it, and refrigerate it for up to two days. Reheat covered at 325°F (165°C) until hot throughout, then uncover and bake briefly to restore the browned top.
Store leftovers in a sealed container in the refrigerator for up to three days. Reheat individual portions in a covered skillet or microwave, though the oven gives the best texture. Freezing is possible, but the dairy may separate slightly and the potatoes can become softer after thawing.
Serving ideas
Potato gratin pairs well with roast chicken, beef tenderloin, pork, baked ham, or a green salad. Because it is rich, serve it with something fresh or acidic, such as dressed bitter greens, roasted broccoli, steamed green beans, or a crisp apple-and-fennel salad.
For clean portions, use a wide spatula and cut down through the layers. Add a final sprinkle of thyme, chives, or black pepper just before serving. If the gratin seems especially rich, offer smaller portions alongside a simply seasoned main course rather than treating it as the only side dish.