Sweet Potatoes au Gratin

A sweet and savory twist on a classic, this Sweet Potatoes au Gratin recipe is sure to steal center stage at your holiday or Thanksgiving table! Thin slices of sweet potatoes are coated in a creamy Gruyere cheese sauce, loaded with TONS of herbs and spices, and finished with a crunchy breadcrumb topping that’s irresistible. Easily meal prep this the day before and pop it in the oven when you’re ready to eat!

Best Sweet Potatoes au Gratin Recipe

Never have I ever seen a dish SO fancy, SO full of flavor, and secretly not TOO complicated to make!

Most of us have had au gratin with white potatoes (Yukon gold potatoes or Russet potatoes) but this sweet potato version is on another level.

What started with a little inspo from these Scalloped Potatoes and Cauliflower Gratin quickly transformed into this burst of Fall flavors.

Shredded Gruyere cheese, fresh thyme and rosemary, and a secret spice (I’ll give you a hint: it starts with a nut- and ends in a -meg!) give the creamy s​auce lots of depth.

But the real kicker comes in at the end. A Panko Parmesan breadcrumb topping counteracts those soft and tender potatoes with a crunchy and salty bite. Bonus—there’s no heavy cream so it’s better for you than many other recipes.

While there are a couple of steps involved, like making the cheese sauce and slicing the potatoes, you can easily prepare the entire dish the day before your big celebration and simply pop it in the oven.

Ingredients

The simple ingredients you need to make this delicious sweet potato au gratin recipe are:

• Sweet potato. There are several varieties available at grocery stores. Try to grab ones that are generally the same size so they can be cut into similar-shaped pieces that cook evenly.
• Butter. Unsalted butter is needed, but you can sub in coconut oil or olive oil, if needed.
• Garlic. Freshly minced garlic creates a rich flavor that perfectly balances the sweetness of the potatoes.
• Flour. You only need a little bit of flour for this recipe. You can either go with regular flour or a gluten-free 1 to 1 blend.
• Milk. Both regular milk and a plant-based alternative will work. The key is to have it at room temperature.
• Cheese. Gruyere cheese and cheddar cheese, both shredded, are sprinkled on top of the potatoes. You’ll also want some Parmesan cheese for the topping.
• Seasonings. Along with salt and pepper, this recipe calls for fresh thyme, rosemary, and ground nutmeg.
• Breadcrumbs. Regular, unseasoned Panko breadcrumbs make the base of the crispy topping. You can grab a gluten-free variety from the grocery store, as well.

How to Make Sweet Potatoes au Gratin

Please see the recipe card below for ingredient amounts and more detailed instructions.

Prep the Potatoes

Preheat the oven to 375℉.

Clean the potatoes by rinsing them under cold running water. Use your hands or a rag to scrub them until no visible dirt or debris remain.

Dry each one off with a clean dish towel.

Then, carefully slice the potatoes into ⅛-inch pieces. The best way to do this is with a mandolin slicer. But you can also use a very sharp chef’s knife.

Line the Potatoes

Spray a 9×13-inch baking or casserole dish with a non-stick cooking spray. 

Layer half of the sweet potato slices across the bottom of the dish. Then, sprinkle ½-teaspoon salt and ¼-teaspoon of black pepper evenly over the top.

Carefully place the rest of the slices in the pan, and top with the remaining salt and pepper.

Make the Sauce

Add the butter to a medium saucepan, and melt it over medium heat. Then, add the minced garlic and sauté for 30 to 60 seconds.

Turn the heat down to medium-low and sprinkle the flour over the melted butter. Whisk immediately. It should form a thick paste.

Then, pour in ¼-cup of the room temperature milk, being sure to whisk it well. After it thickens, add another ¼-cup at a time until it has all been mixed in and the sauce is smooth.

Remove the pot from the stove and stir in the Gruyere cheese, cheddar cheese, fresh herbs, nutmeg, and remaining salt. Stir until the sauce is thoroughly combined.

Coat Potatoes and Bake

Carefully pour the creamy sauce on top of the sweet potatoes in the baking dish. Use a spatula to spread it out so all of the slices are coated.

Cover the dish with a piece of aluminum foil, then bake in the preheated oven for 30 minutes.

Add the Crumb Topping

While the potatoes are baking, add 1 tablespoon of melted butter, ¼-cup Panko crumbs, and ¼-cup Parmesan cheese to a medium bowl. Whisk until it is well combined.

After the 30 minutes, remove the foil from the baking dish and sprinkle the crumb topping evenly over the potatoes. 

Bake for another 15 to 20 minutes. It is done when the topping is golden brown and the potatoes can easily be pierced with a fork.

Serve with some fresh rosemary and thyme!

What’s the difference between au gratin and scalloped potatoes?

While both scalloped and au gratin potatoes are a savory and creamy side, the main difference is the inclusion of cheese in au gratin. Both of these recipes are a perfect side dish for a holiday table or even a weeknight.

What does it mean to cook au gratin?

Gratin simply means to top with cheese, butter, and breadcrumbs and cook until crispy. You can use this method with a variety of foods, like in this Cauliflower au Gratin or these Brussels Sprouts au Gratin!

Dietary Modifications

The recipe you’ll find below is already vegetarian as written. Here are some adjustments and substitutions you can make to help it fit your other dietary requirements:

• Gluten-free: Opt for a gluten-free 1-to-1 blend of flour and gluten-free breadcrumbs.
• Dairy-free: Choose a dairy-free cheese, butter, and milk variety.

What to Serve with Sweet Potato Au Gratin?

This surprisingly simple dish goes well with just about any protein! Try any of these recipes alongside it.

If you’re a fish lover, try Blackened Mahi Mahi or Blackened Salmon.

You can also serve it with Chicken Cordon Bleu, Baked BBQ Chicken, or Caprese Chicken.

More Sweet Potato Recipes

If you prefer sweet potatoes over regular, you’re in luck. These healthy and easy recipes are sure to please your taste buds.

Another fun twist is Sweet Potato Shepherd’s Pie.

At Thanksgiving, whip up some Sweet Potato Casserole and Sweet Potato Pie.

And you can’t get easier than Air Fryer Baked Sweet Potato or Mashed Sweet Potato.

Learn How Healthy Sweet Potatoes are!