Sweet Potato Gratin
Posted Nov 07, 2025
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In this sweet potato gratin recipe, sweet potatoes are sliced thin, layered with onions and baked in a cheesy, homemade sauce. Sweet potatoes au gratin are a flavorful and comforting fall side dish!
If you’re looking for a crowd-pleasing sweet potato side dish that’s delicious and impressive, then you need to make this sweet potato gratin recipe.
The velvety, from-scratch cheese sauce is poured over thinly sliced sweet potatoes and onions then baked to bubbly, golden-brown perfection.
Sweet potatoes au gratin is the perfect holiday or weeknight comfort food that pairs beautifully with everything from meatloaf to Thanksgiving turkey.
Sweet Potato Gratin: Ingredients & Substitutions
- Sweet potatoes: orange, purple and white sweet potatoes all work well in this recipe. Or use this recipe if you’re looking to make traditional au gratin potatoes.
- Sweet Onion. choose your favorite variety: white or yellow.
- Salted butter. unsalted butter is a good substitute.
- Flour. make this recipe gluten-free by using an all-purpose gluten-free flour.
- Whole milk/heavy cream. This sweet potato gratin recipe calls for 2 cups of liquid dairy. You can use all whole milk, all heavy cream, or half and half if you prefer.
- Cheese. This recipe calls for gouda and cheddar cheeses, you can use your favorite cheese.
How to Make Sweet Potato Gratin
Let’s walk through this sweet potato gratin recipe together step-by-step. As always, be sure to watch the video for additional guidance.
Begin by preheating your oven and lightly greasing a 9×13″ baking dish with butter. Then set the dish aside.
Make the Cheese Sauce
The great thing about these au gratin sweet potatoes is that they’re made completely from scratch. So, we begin by making the cheese sauce.
To do this, melt the butter in a medium saucepan over medium heat.
Then add the flour, salt, garlic powder and pepper and whisk to combine.
Cook the roux for about 1 minute, or until the butter bubbles and lightly browns.
Then, whisk in the milk and heavy cream.
Continue cooking the sauce over medium heat, whisking often, until it has thickened (about 2-3 minutes). It will lightly coat the back of a spatula.
Once the sauce is thickened, turn off the heat, add the cheese and whisk over the warm burner until it’s melted and the sauce is smooth.
NOTE: The sauce is very thick!
Assemble the Sweet Potato Gratin
Once the sauce is ready, it’s time ot assemble the sweet potato gratin. Begin by arranging ⅓ of the sweet potatoes in an even layer in the bottom of the prepared baking dish.
Then, top the sweet potatoes with half of the onion slices and lightly sprinkle with salt and pepper.
Top onions with the second third of the sweet potatoes, then top that layer of sweet potatoes with remaining onion slices and salt and pepper
Then, put the final third of the sweet potatoes on top, and season with salt and pepper.
Next, pour the cheese sauce over the top of the potatoes and cover the baking dish with aluminum foil.
Bake the sweet potato gratin in the preheated oven for 50 minutes to 1 hour, or until the sweet potatoes are soft when pricked with a fork (but not mushy).
Once the sweet potatoes are soft, remove the foil and sprinkle the top with 1 cup of cheddar cheese and 1 cup gouda cheese.
Bake the sweet potatoes au gratin on the top rack of your oven, uncovered, for an additional 8 to 10 minutes until the cheese is melted, bubbly and lightly golden brown, the filling should be bubbling, and the sweet potatoes should be tender.
Remove the baking dish from the oven, let cool slightly (uncovered) and serve warm.
Serve
This au gratin sweet potatoes recipe pairs well with many main dish recipes. Here are some suggestions:
- Serve alongside Roast Turkey on the holidays, along with our other Thanksgiving Recipes.
- They’re perfect with slow cooker pot roast.
- Make them with the best meatloaf recipe.
Store/Freeze
Store leftovers in an airtight container in the refrigerator for up to 5 days, or in the freezer for up to 1 month.
Thaw or reheat the sweet potatoes covered in a baking dish in the oven set to warm.
Sweet Potato Gratin Recipe FAQS
The biggest difference between the two dishes is that scalloped sweet potatoes do not traditionally include cheese, while au gratin sweet potatoes do.
Yes, you can slice the sweet potatoes and onions and store them in an airtight container in the refrigerator. Then, you can do the same with the sauce – you can make the sauce and store it in the refrigerator. Then assemble and bake when you want to serve. Or you can make the full recipe including baking – and just reheat when you’re ready to serve.
I am usually a fan of unpeeled sweet potatoes, but not in this recipe. For the best texture I highly recommend peeling.
Here are my top picks for this recipe:
-Gouda
-Medium to sharp cheddar
– Gruyère
– Swiss
For best results, slice them about 1/8-inch thick.
If you make and love my recipes, it would mean so much to me if you would leave a comment and rating! And don’t forget to follow along on Instagram, Pinterest, Facebook, TikTok and Youtube – be sure to tag @joyfoodsunshine and use the hashtag #joyfoodsunshine so I can see your creations!
Sweet Potato Gratin
Video
Equipment
Ingredients
- 3 pounds sweet potatoes (peeled and thinly sliced, about 5 cups)
- 1 medium sweet onion (cut in half then thinly sliced)
- 1 Tablespoon salted butter (for greasing the pan)
Cheese Sauce
- 4 Tablespoons salted butter
- ¼ cup all-purpose flour
- 1 teaspoon fine sea salt
- ½ tsp garlic powder
- ¼ teaspoon black pepper
- ½ cup whole milk
- 1 cup heavy cream
- 1 cup cheddar cheese (shredded)
- 1 cup gouda cheese (shredded)
Topping
- 1 cup grated sharp cheddar cheese
- 1 cup gouda cheese
Instructions
- Preheat oven to 400°Fahrenheit (204 degrees Celsius).
- Lightly grease a 9×13” baking dish with butter, set aside.
Make the Cheese Sauce
- Melt the butter in a medium saucepan over medium heat.
- Add flour, salt, garlic powder and pepper and whisk to combine. Cook for about 1 minute, or until butter bubbles and lightly browns.
- Add milk and heavy cream and whisk to combine.
- Cook the sauce over medium heat, whisking often, until it has thickened (about 2-3 minutes).
- Once thickened, turn off the heat, add the cheese and whisk until melted. Set aside. (it is thick).
Make the Sweet Potato Gratin
- Place ⅓ of the sweet potatoes on the bottom of the prepared pan.
- Top with half of the onion slices, then lightly sprinkle with salt and pepper.
- Top onions with the second third of the sweet potatoes, then top that layer of sweet potatoes with remaining onion slices and salt and pepper
- Then, put the final third of the sweet potatoes on top, and season with salt and pepper.
- Next, pour the cheese sauce over the top of the potatoes.
Bake, Cool & Serve
- Cover the baking dish with aluminum foil and bake in the preheated oven for 50 minutes to 1 hour, or until the sweet potatoes are soft when pricked with a fork (but not mushy).
- Once the sweet potatoes are soft, remove the foil and sprinkle the top with 1 cup of cheddar cheese and 1 cup gouda cheese.
- Bake on the top rack of your oven, uncovered, for an additional 8 to 10 minutes until the cheese is melted, bubbly and starting to turn lightly golden brown, the filling should be bubbling, and the potatoes should be tender.
- Remove from the oven, let cool slightly (uncovered) and serve warm.
Notes
- Sweet potatoes: orange, purple and white sweet potatoes all work well in this recipe. Or use this recipe if you’re looking to make traditional au gratin potatoes.
- Sweet Onion. choose your favorite variety: white or yellow.
- Salted butter. unsalted butter is a good substitute.
- Flour. make this recipe gluten-free by using an all-purpose gluten-free flour.
- Whole milk/heavy cream. This sweet potato gratin recipe calls for 2 cups of liquid dairy. You can use all whole milk, all heavy cream, or half and half if you prefer.
- Cheese. This recipe calls for gouda and cheddar cheeses, you can use your favorite cheese.
Nutrition
Nutrition information is automatically calculated, so should only be used as an approximation.
