Easy Sweet Potato Gratin
Easy Sweet Potato Gratin is a cozy, creamy dish that brings the natural sweetness of tender sweet potatoes together with a rich, cheesy sauce. Thin slices of sweet potato are…
By Ava
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Reading time: 7 min
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Easy Sweet Potato Gratin is a cozy, creamy dish that brings the natural sweetness of tender sweet potatoes together with a rich, cheesy sauce. Thin slices of sweet potato are layered with melted cheese and just the right touch of seasoning, making each bite smooth, cheesy, and comforting.
I love making this gratin for family dinners because it feels special but is surprisingly simple to put together. One of my favorite tricks is to slice the sweet potatoes as thin as possible so they cook evenly and soak up all the delicious flavors from the cheese and cream. It’s a dish that always gets compliments, and I find myself making it over and over through the cooler months.
This gratin works perfectly as a side for a big Sunday roast or any time you want to add a little extra comfort to your meal. I like to serve it fresh out of the oven when the top is golden and bubbly, which always brings a smile to the table. It’s that kind of dish that feels warm and homey with every forkful.
Key Ingredients & Substitutions
Sweet Potatoes: Peel and slice as thinly as you can for even cooking and creamy texture. If you don’t have sweet potatoes, you can try using regular potatoes or a mix of both. Just remember sweet potatoes add natural sweetness and creaminess.
Gruyère Cheese: This cheese melts well and adds a nutty flavor. If Gruyère is hard to find, Parmesan, Fontina, or even mozzarella work as substitutes. Mixing cheeses can add more depth to the flavor.
Heavy Cream & Milk: These make the layers rich and creamy. If you want to lighten it up, swap heavy cream for half-and-half or use all milk, but the dish won’t be quite as rich.
Fresh Herbs: Thyme is classic here, bringing a subtle earthy flavor. Fresh sage, rosemary, or even a pinch of nutmeg can be nice alternatives.
How Do I Get Thin, Even Sweet Potato Slices for a Perfect Gratin?
Slicing sweet potatoes evenly is key to this gratin’s creamy texture and even cooking. Here’s how to slice like a pro:
- Use a sharp knife or a mandoline slicer if you have one—it’s perfect for thin, consistent slices.
- Peel the sweet potatoes first, then hold them steady on a cutting board for safety.
- Try to slice about 1/8 inch (3mm) thick so the potatoes cook through and layer nicely.
- If you don’t have a mandoline, cut carefully and steadily with a sharp knife, keeping slices uniform.
- As you slice, you can place slices in cold water to prevent sticking if you’re prepping in advance, but dry them well before layering.
Thin, even slices allow the cream and cheese to soak into each layer, making the gratin rich and tender all the way through. This step really makes a difference!
Equipment You’ll Need
- Sharp knife or mandoline slicer – for thin, even sweet potato slices that cook perfectly.
- Medium saucepan – to warm the cream and infuse it with garlic and herbs gently.
- Butter or oil – to grease the baking dish and prevent sticking.
- Baking dish (around 8×8 inches or similar) – the right size helps layers cook evenly and the top browns nicely.
- Aluminum foil – to cover the dish during baking and keep moisture in for tender potatoes.
- Oven mitts – for safely handling the hot gratin dish straight from the oven.
Flavor Variations & Add-Ins
- Add cooked crumbled bacon or pancetta for a smoky, salty twist that balances the sweet potatoes.
- Swap Gruyère for sharp cheddar or mozzarella for a different cheesy flavor, great if you want something milder or stretch what you have on hand.
- Mix in thinly sliced onions or leeks between layers for extra sweetness and a soft bite.
- Sprinkle a pinch of smoked paprika, nutmeg, or cumin into the cream to add warm, subtle spice notes that deepen the flavor.
Easy Sweet Potato Gratin
Ingredients You’ll Need:
Main Ingredients:
- 3 large sweet potatoes, peeled and thinly sliced
- 1 cup heavy cream
- 1 cup whole milk
- 2 cups shredded Gruyère cheese (or a mix of Gruyère and Parmesan)
- 2 garlic cloves, minced
- 1 teaspoon fresh thyme leaves (plus extra for garnish)
- Salt and freshly ground black pepper, to taste
- 1 tablespoon butter (for greasing the baking dish)
- Optional: Fresh sage leaves for garnish
How Much Time Will You Need?
This recipe takes about 15 minutes to prepare and about 1 hour to bake, including resting time. You’ll spend a short time peeling and slicing the sweet potatoes, gently warming the cream mixture, and layering the ingredients. Baking the gratin covered helps the potatoes soften, then uncovering it lets the top turn golden and bubbly. Finally, resting the dish for 10 minutes before serving lets it set perfectly.
Step-by-Step Instructions:
1. Preheat and Prepare:
Start by preheating your oven to 375°F (190°C). Butter a medium-sized baking dish lightly to keep the gratin from sticking as it bakes.
2. Warm the Cream Mixture:
In a small saucepan, mix together the heavy cream, whole milk, minced garlic, and fresh thyme leaves. Heat it gently over low heat until it almost simmers, then remove from the heat and set aside. This helps the flavors blend.
3. Layer the Sweet Potatoes:
Place a layer of thinly sliced sweet potatoes evenly across the bottom of the baking dish. Sprinkle some shredded Gruyère cheese over the potatoes, then season lightly with salt and pepper.
4. Add Cream and Repeat Layers:
Pour a little of the warm cream mixture over the first layer, just enough to moisten the slices. Repeat layering potatoes, cheese, seasoning, and cream until all ingredients are used, finishing off with a generous layer of cheese on top.
5. Bake Covered, Then Uncovered:
Cover the dish with aluminum foil and bake for about 40 minutes to soften the sweet potatoes. Then remove the foil and bake for another 20 minutes or until the top looks beautifully browned and bubbly. Test by poking the potatoes with a fork—they should be tender.
6. Rest and Serve:
Take the gratin out of the oven and let it rest for about 10 minutes. This helps it set for easier serving. Garnish with fresh thyme and sage leaves if you like, then enjoy your warm, creamy, cheesy sweet potato gratin!
Can I Use Frozen Sweet Potato Slices for This Gratin?
It’s best to use fresh sweet potatoes for this recipe because frozen slices may release extra water and affect the texture. If you do use frozen, thaw them completely and pat dry before layering to avoid sogginess.
How Can I Make This Gratin Ahead of Time?
You can assemble the gratin up to step 6, then cover and refrigerate it for up to 24 hours before baking. When ready, bake covered for about 50 minutes and then uncover for the final 20 minutes to brown the top.
What Are Good Cheese Substitutes if I Don’t Have Gruyère?
Gruyère is ideal for its meltability and flavor, but you can use a mix of Parmesan and mozzarella or even sharp cheddar. Just keep in mind that some cheeses melt differently and can change the flavor profile.
How Should I Store and Reheat Leftovers?
Store leftovers in an airtight container in the fridge for up to 3 days. Reheat gently in the oven at 350°F (175°C) until warmed through to keep the creamy texture, or microwave in short bursts stirring in between.