Imagine sinking your fork into layer after layer of thin-sliced potatoes, all baked to bubbly perfection with a lusciously creamy, cheesy sauce—welcome to pure comfort in a casserole dish, and the irresistible world of Au Gratin Potatoes. This recipe pulls together everything you love about classic side dishes: a golden, crisp top, an impossibly velvety interior, and just the right punch of flavor from Gruyere, Parmesan, caramelized onions, and fresh herbs. If you’re craving something completely satisfying (and quite the showstopper for a crowd!), you’re about to fall in love with these Au Gratin Potatoes.

Au Gratin Potatoes Recipe - Recipe Image

Ingredients You’ll Need

The secret to unforgettable Au Gratin Potatoes lies in just a handful of simple ingredients. Each one brings something magical to the table, whether it’s the creamy decadence of heavy cream or the nutty sharpness of Gruyere. Here’s why you don’t want to swap a thing:

Yellow Onion: Caramelized onions add layers of sweetness and depth you’ll taste in every bite.
Salted Butter: Enriches the sauce and helps those onions turn perfectly golden and soft.
Fresh Garlic: Freshly minced is key—it brings a gentle heat and aroma no jarred garlic can match.
Fresh Thyme Leaves: Just the right herbal note for cutting through all the creaminess.
Heavy Cream: Essential for that signature silky-smooth texture in your sauce.
Milk: Adds a bit of lightness to balance the cream, making the dish luscious without becoming too heavy.
Gruyere Cheese: Melts beautifully for a subtle, elegant, nutty flavor—don’t skip it!
Parmesan Cheese: Lends a sharp, salty kick to help the flavors really sing.
Salt and Pepper: Simple, but absolutely necessary to make those flavors pop.
Russet Potatoes: The classic choice for Au Gratin Potatoes—their high starch content thickens the sauce and soaks up flavor.
Chives: That fresh, green garnish adds a pop of color and a hint of oniony brightness at the end.

How to Make Au Gratin Potatoes

Step 1: Caramelize the Onions

Start by grabbing a soup pot and melting salted butter over medium heat. Add your finely diced yellow onion and be patient for about 10 minutes, stirring often. Once they’re soft, lower the heat to medium-low and keep sautéing, stirring frequently, for another 10 to 15 minutes until the onions turn beautifully golden and just begin to caramelize. This step makes all the difference by deepening the savory base of your Au Gratin Potatoes.

Step 2: Add Garlic and Thyme

Once the onions look sticky and sweet, stir in the freshly minced garlic and thyme leaves. Let them sizzle for 2 minutes, just until everything smells absolutely incredible. These aromatic bits infuse the sauce, giving every forkful a lovely, herbaceous undertone.

Step 3: Warm the Cream and Milk

While your onions are caramelizing, combine the heavy cream and milk in a microwave-safe cup or bowl. Pop it in the microwave for one minute—just enough to take off the chill. This not only helps your sauce come together more smoothly but also ensures it won’t seize when you add it to the hot pan.

Step 4: Build the Cheese Sauce

Take the onion pot off the heat for a moment, then gently pour in your warmed cream and milk. Give everything a good stir, set the heat to medium-high, and bring the mixture up to a gentle boil before removing from the heat again. Now slowly add the Gruyere and Parmesan, letting each handful melt before adding the next. Season with salt and pepper—suddenly, you’ll have a dreamy sauce that’s the soul of these Au Gratin Potatoes.

Step 5: Slice the Potatoes

This is where your mandoline slicer earns its keep! Scrub and peel your russet potatoes, then slice them into thin, 1/8-inch rounds. Consistency is key so they all cook tender at the same rate. If you don’t have a mandoline, use a sharp knife as carefully as possible. Trust me—thin is best for that perfect creamy bite.

Step 6: Assemble the Layers

Preheat your oven to 350°F. Lightly grease a 2.5-quart or 9×13-inch baking dish, then fan out one-third of the potato slices across the bottom. Lightly sprinkle with salt, then spoon over one-third of the cheese sauce. Repeat this for two more layers, finishing with sauce on top. This creates those show-stopping pockets of gooey sauce and melting cheese throughout the dish.

Step 7: Bake Covered, Then Uncovered

Cover your baking dish tightly with foil and bake for an hour. Then, remove the cover and bake for another 30 minutes. For an irresistible golden crust, crank your oven up to broil at 425°F for 1-2 minutes, keeping a close eye so nothing burns. Let your Au Gratin Potatoes rest for at least 5-10 minutes before you dig in—this allows the sauce to thicken and settle, making it extra luscious.

How to Serve Au Gratin Potatoes

Garnishes

To finish your Au Gratin Potatoes in style, shower over a handful of chopped fresh chives. Their bright flavor and vibrant green color add a fresh contrast to all the rich, cheesy layers. For a bit of crunch, you could sprinkle on some crispy fried shallots or extra Parmesan before serving.

Side Dishes

These Au Gratin Potatoes shine next to so many main courses—they’re classic with roast beef, ham, or baked chicken, but also gorgeously cozy with simple sautéed greens. Add a crisp salad with a tangy vinaigrette, or serve with steamed broccoli to balance out all those creamy, cheesy layers.

Creative Ways to Present

For an elegant twist, portion your Au Gratin Potatoes into individual ramekins before baking so everyone gets their own tiny casserole. Or, use a cookie cutter to cut out neat rounds from the finished dish for a party-worthy presentation. Top each serving with a little dollop of crème fraîche and more herbs for a restaurant-style finish!

Make Ahead and Storage

Storing Leftovers

Leftover Au Gratin Potatoes are wonderfully forgiving. Simply transfer any extras to an airtight container and refrigerate for up to five days. The flavors deepen as they sit, making every reheated bite possibly even better than the first!

Freezing

You can freeze your Au Gratin Potatoes, but just a heads-up—the creamy sauce can separate a bit when thawed and reheated. If you do freeze portions, wrap them tightly in both foil and plastic wrap, and use within one month for best texture.

Reheating

To bring leftovers back to life, place the potatoes in a baking dish, cover with foil, and warm at 350°F until hot and bubbly. For smaller servings, the microwave works too, though you might want to splash over a bit of extra cream before heating to keep them creamy.

FAQs

Can I use a different type of cheese in Au Gratin Potatoes?

Absolutely! While Gruyere is the classic pick for its perfect melt and flavor, a good quality sharp cheddar or even Fontina can work well in a pinch. Consider adding a touch of smoked Gouda for complexity, but Gruyere really sets these Au Gratin Potatoes apart.

Do I have to peel the potatoes?

Peeling is highly recommended for classic Au Gratin Potatoes—removing the skins ensures every layer is perfectly soft and lets the creamy sauce soak in properly. If you use Yukon Golds, you might leave some skin on for a rustic look, but russets are best peeled.

How can I prevent my potatoes from turning brown while slicing?

As you slice your potatoes, place them in a bowl of cold water to keep them from oxidizing and turning brown. Just remember to pat them dry before layering so the sauce doesn’t get watery.

What if I don’t have a mandoline slicer?

No problem! A sharp chef’s knife will do the job; just try your best to cut the potatoes into uniform, thin slices—about 1/8-inch thick is perfect for even cooking and that signature texture in your Au Gratin Potatoes.

Can I assemble Au Gratin Potatoes ahead of time?

Definitely! You can assemble and partially bake the dish up to two days in advance. Let cool completely, then cover and refrigerate. When ready to serve, simply finish baking as described above, and your Au Gratin Potatoes will be every bit as satisfying and creamy.

Final Thoughts

If you’re on the hunt for the ultimate cozy side, this recipe for Au Gratin Potatoes promises comfort and genuine wow-factor bite after bite. From special occasions to Sunday dinners, it’s the kind of dish that quickly becomes a go-to classic. Gather your ingredients, slice those potatoes, and get ready to make an old-fashioned favorite that everyone will be talking about!