The secret to a good potato gratin is in the technique, and this one is simple. To start, thinly sliced potatoes (plus other root vegetables, if you like) are simmered in seasoned liquid (cream, milk, broth, or a combination) until barely tender. After that, the potatoes are layered in a casserole dish with flavor boosters (such as fresh herbs, sautéed vegetables, grated cheese, crisp bacon), and topped with breadcrumbs, cheese, or nuts. A quick bake and you’re done.
The advantages to this method are several: simmering gives the potatoes more opportunity to soak up flavor; starches are released into the liquid earlier, which helps prevent curdling during baking; and the top layer of the potatoes remains moist.
There are only three fundamental components to any potato gratin—the potatoes, the liquid, and the top crust. The best gratin potatoes are medium-starch, buttery Yukon Golds. As opposed to russets, which drink up all the liquid and make a drier gratin, and waxy potatoes, which don’t absorb enough, Yukon Golds soak up plenty of liquid but still leave discernible layers in your finished gratin.
Finally, in order to qualify as a gratin, the casserole needs a top crust. You can make it simple with a scattering of breadcrumbs and cheese, or you can add your favorite nuts for crunch. See below for options.
It’s important to read the entire method through before you start so you can decide which optional ingredients you want in your gratin.
The whole gratin serves 8
Prep the potatoes (and root veggies)
All of these gratins start with layers of tender, sliced Yukon Gold potatoes. But if you like, you can supplement the potatoes with other root vegetables, as long as you have 2 to 2-1/2 lb. total.
Position a rack in the center of the oven and heat the oven to 400°F. Butter or oil a 3-quart gratin dish; set aside.
Peel and slice 2 to 2-1/2 lb. Yukon Gold potatoes OR use one of the potato-root vegetable combinations below.
Choose your potato base
Add the liquids
For a classic gratin—rich, creamy, indulgent—heavy cream is key. But you can also use light cream, or a mixture of cream and milk. An all-milk or milk-broth gratin will tend to curdle, but you can go with all-broth for the lightest option.
Put the potatoes (and root vegetables, if using) in a 12-inch skillet with 2-1/2 cups liquid (see options below). Add 1/2 tsp. kosher salt and a few grinds of black pepper. Simmer, partially covered, over medium to medium-low heat, stirring occasionally and gently with a rubber spatula until barely tender when pierced with a fork or skewer, 8 to 12 minutes. Add another 1/2 to 3/4 tsp. salt if you’re not adding any other salty ingredients in the next steps (such as bacon, cheese, or well-seasoned sautéed vegetables).
Choose one or more liquids for a total of 2-1/2 cups
Prep meat add-ins (if using)
A salty cured meat like pancetta or bacon isn’t essential, but it gives the gratin another layer of flavor.
If you’ve chosen ham, Canadian bacon, or proscuitto for your meat (see choices below), they need no pre-cooking. If you’ve chosen bacon, pancetta, or sausage, heat a large skillet over medium-high heat, add 4 to 6 oz. meat (optional; see choices below) and cook until browned and fully cooked. Transfer to a plate. If you’re using bacon or pancetta, reserve 2 Tbs. of the drippings for cooking the vegetables in the next step. If using bacon or sausage, crumble it when it’s cool.
Choose a meat (optional)
Prep vegetable add-ins (if using)
These vegetables get sautéed until tender and then layered between the root vegetables. Just make sure anything you choose here complements your potato base.
Heat 1 or 2 Tbs. butter, oil, or bacon or pancetta fat in a large skillet over medium-high. Add your chosen vegetable (see options below), and sauté until tender and lightly browned. Season to taste with salt and pepper. If using more than one vegetable, sauté each separately (except for garlic, which can be combined with another vegetable at the end of cooking.)
Choose up to 3 vegetables (optional)
Layer your ingredients
A jolt of fresh green herbs or a sharp spice can help break up the overwhelming richness of the gratin. If you want to add cheese, keep in mind that Gruyère is a classic addition, but other cheeses will bring new dimensions and are worth trying.
Using a slotted spoon, transfer half the potato/root vegetables to the gratin dish, spreading them evenly. Layer on your meat and cooked vegetables, 6 oz. of your chosen cheese (optional; see choices below), and your choice of herbs or spices (see options below), arranging them evenly on top of the potatoes. Top with the remaining potatoes/root vegetables, spreading them evenly, and pour over any liquid remaining in the pan.
Choose up to 2 cheeses for a total of 6 oz. (optional)
Choose 2 to 4 herbs and spices
Top & bake
To qualify as a gratin, the casserole should have a top crust. Traditionally, this is a scattering of breadcrumbs and cheese, but sprinkling the gratin with an optional topping like chopped nuts is another alternative for both added texture and flavor.
Combine your topping choices (see options below) in a small bowl. Evenly scatter your choice of toppings over the potatoes.
Bake the gratin until it’s bubbly, the top is brown, and the potatoes are completely tender when poked with a fork or skewer, 25 to 30 minutes. Let the gratin sit for at least 10 and up to 30 minutes before serving so the liquid is fully absorbed and the layers are cohesive.
Choose your topping
How to prep leftovers: You can store tightly wrapped leftovers in the refrigerator for up to 2 days. To reheat, cover with foil and bake in a 350°F oven for about 30 minutes.
How to cut the serving size: A whole gratin serves eight. To feed fewer people, follow the method, cutting all the amounts in half. Use a tightly covered 10-inch skillet to simmer the potatoes, and bake in a 1-1/2-quart baking dish.