Irresistible Sweet Potato Gratin with Cream and Thyme

This Irresistible Sweet Potato Gratin with Cream and Thyme is a cozy, creamy dish that's perfect for any time you're craving something comforting. The sweet potatoes are thinly sliced and…

By Julia • October 31, 2025 • Reading time: 6 min

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This Irresistible Sweet Potato Gratin with Cream and Thyme is a cozy, creamy dish that’s perfect for any time you’re craving something comforting. The sweet potatoes are thinly sliced and layered with rich cream and fresh thyme, creating a tender, flavorful bake with a golden, bubbly top that’s hard to resist.

I love how the thyme adds just the right touch of earthiness to balance the sweetness of the potatoes. It’s simple to put together but always feels like a special treat. When I make this, I usually let it sit for a few minutes after baking so the flavors can settle and the cream thickens up just a bit—it makes the gratin even better.

This dish works wonderfully as a side for a family dinner or gathering, especially alongside roasted meats or a fresh salad. I find that it’s also great warmed up the next day, so I always make a little extra. It’s just one of those comfort foods that everyone seems to love, and it always gets compliments whenever I bring it to the table.

Key Ingredients & Substitutions

Sweet Potatoes: Thinly sliced sweet potatoes are the star here. If you can’t find sweet potatoes, you can swap in yams or even regular potatoes, but the flavor will be less sweet and more earthy.

Heavy Cream & Milk: These add richness and creaminess. For a lighter option, use half-and-half or a mix of milk and Greek yogurt, though the texture will be less silky.

Thyme: Fresh thyme adds a nice herbal note that pairs perfectly with the sweetness. If fresh isn’t available, dried thyme works too—use about one-third the amount.

Gruyère Cheese: This is optional but adds a lovely nutty flavor and helps create a golden crust. If you want a simpler or dairy-free version, leave it out or substitute with mozzarella or vegan cheese.

How Do You Get Perfect, Even Slices for a Smooth Gratin?

Thin, even slices cook more quickly and help your gratin bake evenly. Here’s how I do it:

• Use a mandoline slicer if you have one—it makes uniform slices about 1/8 inch thick.
• No mandoline? Use a sharp knife and take your time slicing carefully.
• Try to slice all potatoes to similar thickness so they cook evenly.
• If slices vary too much, some may overcook while others stay firm.

Taking these simple steps ensures your gratin has a tender, melt-in-your-mouth texture throughout, without any crunchy or undercooked bits.

Equipment You’ll Need

• Mandoline slicer – helps you get thin, even sweet potato slices quickly and safely.
• 9×13-inch baking dish – perfect size for layering and baking the gratin evenly.
• Medium saucepan – for warming the cream mixture without boiling.
• Wooden spoon or heatproof spatula – great for stirring the cream and garlic blend gently.
• Aluminum foil – to cover the dish while baking, keeping moisture in for tender potatoes.

Flavor Variations & Add-Ins

• Add shredded sharp cheddar or Parmesan cheese instead of Gruyère for a tangy twist.
• Mix in sautéed onions or caramelized leeks for extra sweetness and depth.
• Stir in some crispy cooked bacon or pancetta for a smoky, savory note.
• Swap thyme for rosemary or sage to change the herbal flavor profile.

Irresistible Sweet Potato Gratin with Cream and Thyme

Ingredients You’ll Need:

Main Ingredients:

• 3 large sweet potatoes (about 2 pounds), peeled and thinly sliced
• 2 cups heavy cream
• 1 cup whole milk
• 2 cloves garlic, minced
• 3 tablespoons unsalted butter, plus extra for greasing the dish
• 1 teaspoon fresh thyme leaves, plus extra sprigs for garnish
• 1 cup Gruyère cheese, grated (optional for extra richness)
• ½ teaspoon salt
• ¼ teaspoon freshly ground black pepper
• Pinch of freshly grated nutmeg (optional)

How Much Time Will You Need?

This delicious gratin takes about 15 minutes to prepare, including peeling and slicing the sweet potatoes and making the cream sauce. Baking time is approximately 70 to 75 minutes, with 45 minutes covered and an additional 25-30 minutes uncovered to achieve a bubbly, golden top. Don’t forget to set aside about 10 minutes to let the gratin rest before serving.

Step-by-Step Instructions:

1. Prepare the Oven and Dish:

Preheat your oven to 375°F (190°C). Grease a 9×13-inch baking dish well with butter to prevent sticking and add delicious richness.

2. Slice the Sweet Potatoes:

Peel the sweet potatoes and slice them very thinly—about 1/8 inch thick. Using a mandoline slicer makes this easier and ensures even cooking. Take your time if slicing by hand to keep slices consistent.

3. Make the Cream Mixture:

In a medium saucepan over medium heat, combine the heavy cream, milk, minced garlic, butter, thyme leaves, salt, pepper, and the optional nutmeg. Warm this mixture gently until the butter melts and the mixture is hot but not boiling. Remove from heat immediately.

4. Layer the Sweet Potatoes and Cream:

Arrange a layer of sweet potato slices in the bottom of your prepared dish, overlapping them slightly. Pour enough of the warm cream mixture over the potatoes to just cover them. If desired, sprinkle a portion of the Gruyère cheese over this layer.

5. Repeat Layers and Top:

Continue layering remaining sweet potatoes, cream mixture, and cheese, finishing with a final layer of sweet potatoes topped with cream. This layering creates that classic gratin richness and beautiful texture.

6. Bake Covered:

Cover the dish tightly with aluminum foil and bake for 45 minutes. This helps the sweet potatoes cook through while keeping moisture in.

7. Bake Uncovered for a Golden Finish:

Remove the foil and bake for another 25-30 minutes, or until the top is golden brown, bubbly, and sweet potatoes are tender when pierced with a knife.

8. Rest and Serve:

Let the gratin rest for about 10 minutes before serving to allow it to set and for flavors to meld. Garnish with fresh thyme sprigs right before serving for a fresh, pretty touch.

Enjoy this creamy, comforting sweet potato gratin as a delightful side dish that pairs beautifully with roasted meats or a crisp green salad!

Can I Use Frozen Sweet Potatoes for This Gratin?

It’s best to use fresh sweet potatoes because frozen ones can release extra moisture, making the gratin watery. If you only have frozen, thaw them completely and pat dry thoroughly before slicing and layering.

Can I Make This Sweet Potato Gratin Ahead of Time?

Absolutely! Prepare the gratin up to the baking step, cover it tightly, and refrigerate for up to 24 hours. When ready, bake covered for about 50 minutes, then uncover and finish baking until golden and bubbly.

How Should I Store Leftovers?

Store leftover gratin in an airtight container in the refrigerator for up to 3 days. Reheat gently in the oven at 350°F (175°C) until warmed through to maintain the creamy texture.

What Can I Serve with Sweet Potato Gratin?

This gratin pairs wonderfully with roasted chicken, pork, or beef, and goes nicely alongside a fresh green salad or steamed vegetables for a balanced meal.