Farro Potato Gratin with Creamy Layers and Crisp Top

Farro potato gratin layers tender potatoes and chewy, nutty farro in a thyme-scented cream sauce, finished with browned cheese. It is a satisfying oven-baked side or vegetarian main, with the grains adding texture and substance to the familiar creamy potato casserole.

Ingredients

1 cup (200 g) pearled farro
2 teaspoons (10 g) fine salt, divided, plus more for the farro water
2½ pounds (1.13 kg) Yukon Gold potatoes
1½ cups (360 ml) heavy cream
1 cup (240 ml) whole milk
2 tablespoons (28 g) unsalted butter, plus a little extra for greasing the dish
2 garlic cloves (about 6 g), finely grated or minced
1 teaspoon (1 g) fresh thyme leaves, or ½ teaspoon (0.5 g) dried thyme
⅛ teaspoon (0.25 g) freshly grated nutmeg
½ teaspoon (1 g) black pepper
1½ cups (150 g) grated Gruyère cheese
½ cup (50 g) finely grated Parmesan cheese

Instructions

Get set up and prepare the potatoes. Set a rack in the middle of the oven and heat it to 375°F (190°C). Butter a 9-by-13-inch (23-by-33-cm) baking dish. Rinse the farro in a fine-mesh strainer. Scrub or peel the potatoes, as you prefer, and slice them crosswise into even rounds about ⅛ inch (3 mm) thick. A mandoline makes uniform slices quickly, but a sharp knife works; use a guard if you have one and keep your fingertips clear. Grate the cheeses and measure the remaining ingredients. Allow about 25 minutes for this preparation and about 10 minutes later for layering.
Cook the farro. Put the farro in a saucepan with 3 cups (710 ml) water and a generous pinch of salt. Bring it to a boil, then lower the heat to maintain a steady simmer. Cook pearled farro for about 25 minutes, stirring once or twice, until tender but still pleasantly chewy. Drain it thoroughly. Farro brands and harvests vary, so begin checking at 20 minutes; if the grains remain hard at the center, simmer a little longer and drain when ready. Do not cook it until mushy, since it will continue to soften in the oven.
Warm the cream mixture. While the farro cooks, combine the cream, milk, butter, garlic, thyme, nutmeg, pepper, and the remaining 2 teaspoons (10 g) salt in a small saucepan. Warm over low heat for 3 to 4 minutes, stirring until the butter melts and the mixture is steaming. Do not let it boil hard. Warming helps the butter and seasonings distribute evenly and gives the chilled potatoes a head start, but the liquid need not be hot. Take the pan off the heat.
Build the layers. Arrange about one-third of the potato slices in the buttered dish, overlapping them slightly. Scatter half of the cooked farro and about one-third of the Gruyère over the potatoes. Repeat with another third of the potatoes, the remaining farro, and another third of the Gruyère. Finish with the last potatoes. Slowly pour the warm cream mixture evenly over the dish, nudging the top layer gently so liquid can run between the slices. Sprinkle the remaining Gruyère and all the Parmesan over the surface. If the farro clumps as you add it, separate the grains with a fork so they are spread through the gratin rather than concentrated in a few spots.
Bake covered until the potatoes are nearly tender. Cover the dish tightly with foil and bake for 35 minutes. The foil traps steam so the potatoes cook through before the cheese topping browns. Remove the dish carefully; hot steam can escape when you lift the foil. Test a potato near the center with the tip of a small knife. It should be softening but may still offer slight resistance. If it is still quite firm, cover again and bake for 5 to 10 minutes before moving on.
Brown the top. Remove the foil and bake for another 20 minutes, until the top is golden in spots and a knife slides easily through the potatoes in the center. The cream should be bubbling around the edges, and the farro should look plump rather than dry. Ovens and slice thickness vary; if the potatoes need more time, loosely cover the dish again so the cheese does not get too dark, and bake in 5-minute increments. If the surface is cooked but not browned, use the broiler for 1 to 2 minutes, watching continuously.
Rest before serving. Set the gratin on a heatproof surface and let it stand for 15 minutes. This rest allows the cream to settle and thicken, making the portions easier to lift and less likely to run across the plate. Serve warm, spooning up the creamy farro and potatoes from the bottom as well as the crisp, cheesy top.

Tips

Choose pearled farro for this timing. Pearled farro has some of its bran removed, so it cooks sooner than whole farro. Semi-pearled farro can work, but check the package and allow extra simmering time if needed. Whole farro may take substantially longer and can stay too firm in the gratin if it is not cooked until tender first. The grain should be chewy, not crunchy, before it goes into the baking dish.
Slice the potatoes evenly. Thin, consistent slices cook at the same pace and make neat layers. Thick or irregular pieces can leave firm pockets in the center while the edges become soft. If you slice the potatoes ahead, keep them submerged in cold water to prevent browning, then drain and dry them well before layering; extra water can dilute the cream.
Season the layers, not just the sauce. The measured salt seasons the cream and potatoes, but the cheese also contributes saltiness. If your Parmesan is particularly salty, use a little less and taste the warm cream mixture before assembling. Avoid adding extra salt at the table until you have tasted a serving.
Use a practical cheese swap if needed. Gruyère melts smoothly and brings a mild, nutty flavor. Swiss cheese or Comté can stand in at the same quantity; Swiss is usually milder, while Comté is similarly savory. If neither is available, use a good melting cheese such as white cheddar, though the gratin will taste sharper and less traditionally nutty. Keep the Parmesan for its salty, browned finish.

Serving Suggestions

Serve this gratin as a substantial vegetarian centerpiece with a crisp green salad dressed in a bright vinaigrette. The acidity in the dressing balances the rich cream and cheese, while greens such as arugula, little gem, or chopped romaine add a fresh contrast. Roasted broccoli, green beans, or Brussels sprouts also make useful sides, especially for a holiday or cool-weather dinner.

For a larger meal, offer it alongside roast chicken, pork, or a simple baked fish, keeping the other sides relatively light. A modest square is filling because the potatoes, farro, cream, and cheese all have plenty of presence. Let the dish rest before portioning, then use a broad spatula to lift pieces without breaking every layer. A little chopped parsley or extra thyme can brighten the top just before serving, but is optional.

Variations

Add vegetables: Fold 1 cup (about 150 g) of sautéed mushrooms into the cooked farro for an earthy variation. Cook off their moisture first so they do not water down the sauce. Thinly sliced leeks can also be softened in a little butter and layered with the potatoes; let them cool slightly before assembling. Keep additions moderate, since a very full dish takes longer to heat through.

Change the herbs or cheese: Rosemary can replace the thyme, but use a light hand because its flavor is more assertive. A small pinch of mustard powder stirred into the cream gives the cheese a savory edge. For a sharper finish, replace some of the Gruyère with mature cheddar. These are flexible home-style variations rather than requirements; the basic combination of potato, farro, cream, and cheese is the point.

Make it without dairy: Use an unsweetened, unflavored oat cooking cream and a plant-based butter, and choose a dairy-free melting cheese if desired. The result will not have quite the same richness or browned cheese flavor, and products vary in how they behave in the oven. Check the gratin earlier than the stated finish time, and add a little warm vegetable stock if the sauce looks unusually thick before baking.

Use a different grain: Barley can replace farro in equal measure, but it contains gluten and may need a different simmer time, so cook it until chewy and tender according to its package before layering. Quinoa is another option and cooks more quickly, but it is smaller and softer, giving the dish a less chewy texture. For either swap, drain thoroughly and keep the total cooked grain amount similar.

Storage and Reheating

Let leftovers cool briefly, then refrigerate them within 2 hours of cooking in a covered container or tightly covered baking dish. Refrigerated gratin keeps for 3 to 4 days. For easier reheating, divide it into individual portions once it is cool. The potatoes will firm up in the refrigerator, and the sauce may look thicker; that is normal.

Reheat a portion covered in a 350°F (175°C) oven until hot throughout, usually 20 to 30 minutes depending on its size and whether it starts cold. Uncover it for the last 5 minutes if you want to refresh the browned top. A microwave also works for a single serving: cover loosely and heat in short intervals, turning or checking between intervals so the center warms evenly. Reheat leftovers to 165°F (74°C), checking the center with a food thermometer. Avoid repeatedly cooling and reheating the whole dish; warm only the portions you plan to eat.

To freeze, wrap fully cooled portions airtight and freeze for up to 2 months for best quality. Thaw overnight in the refrigerator, then reheat covered in the oven until hot throughout. The potatoes can become somewhat softer and the cream sauce may separate slightly after freezing, but a gentle oven reheat generally brings the dish back together. Do not leave the gratin at room temperature for more than 2 hours.

Frequently Asked Questions

Do I need to cook the farro before baking the gratin?
Yes. The farro is simmered separately until tender, then drained and layered into the dish. Raw farro would need more liquid and a much longer, less predictable baking time than the potatoes, so cooking it first helps both components finish together.

Can I use whole farro instead of pearled farro?
You can, but whole farro usually takes longer to soften. Cook it according to its package directions until chewy and tender before adding it to the gratin, and expect the preparation to take longer than the listed timing. Do not rely on the oven bake alone to cook whole farro properly.

Can I assemble the gratin ahead?
For the best potato texture, cook the farro and prepare the cream mixture ahead, then slice and layer the potatoes shortly before baking. If you assemble the whole dish in advance, cover and refrigerate it, then bake it within 24 hours. It will start cold, so allow extra oven time and check that the center potatoes are tender before serving.

Why are my potatoes still firm in the middle?
They may be sliced too thick, packed into uneven layers, or not baked long enough. Cover the dish again and continue baking in 5- to 10-minute increments until a knife passes through the center easily. Check that the foil was fitted tightly during the first stage, since that trapped steam helps cook the potatoes.

Can I make this gratin without Gruyère?
Yes. Swiss cheese, Comté, or a mild white cheddar can replace it in the same amount. The flavor and browning will differ slightly, but the dish will still work. Keep the Parmesan if you can, since it adds a salty, savory layer to the top.

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