📝 About This Recipe
This elegant twist on a classic French gratin elevates the humble sweet potato into a luxurious masterpiece of flavor and texture. Bathed in a velvety, garlic-infused cream sauce and layered with nutty Gruyère cheese, these potatoes are slow-baked until tender with a golden, bubbling crust. It is the ultimate comforting side dish that perfectly balances the natural sweetness of the tubers with savory herbs and rich dairy.
🥗 Ingredients
The Potatoes
- 3 pounds Sweet Potatoes (peeled and sliced into 1/8-inch thick rounds)
- 2 tablespoons Unsalted Butter (softened, for greasing the baking dish)
The Cream Sauce
- 2 cups Heavy Cream (full fat for the best consistency)
- 1/2 cup Whole Milk
- 3 cloves Garlic (minced very finely)
- 1 tablespoon Fresh Thyme (leaves stripped from stems)
- 1.5 teaspoons Kosher Salt (adjust to taste)
- 1/2 teaspoon Black Pepper (freshly cracked)
- 1/4 teaspoon Nutmeg (freshly grated is preferred)
Cheese & Topping
- 1.5 cups Gruyère Cheese (shredded)
- 1/2 cup Parmesan Cheese (finely grated)
- 1 large Shallot (finely minced)
- 2 tablespoons Fresh Chives (chopped, for garnish)
👨🍳 Instructions
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1
Preheat your oven to 375°F (190°C). Generously grease a 9x13 inch ceramic or glass baking dish with the softened butter, ensuring you coat the corners well.
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2
Peel the sweet potatoes and slice them into uniform 1/8-inch thick rounds. Using a mandoline is highly recommended to ensure even cooking.
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3
In a medium saucepan over medium heat, combine the heavy cream, whole milk, minced garlic, and minced shallots.
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4
Bring the cream mixture to a very gentle simmer (do not let it boil rapidly). Stir in the fresh thyme, salt, pepper, and nutmeg.
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5
Remove the sauce from the heat and let it steep for 5 minutes to allow the aromatics to infuse the cream.
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6
Begin layering: Place about one-third of the sweet potato slices in the bottom of the prepared dish, overlapping them slightly like shingles.
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7
Sprinkle one-third of the shredded Gruyère cheese over the first layer of potatoes.
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8
Repeat the layering process twice more with the remaining potatoes and Gruyère, ending with a final layer of potatoes on top.
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9
Carefully pour the warm cream mixture over the potatoes. Gently press down on the potatoes with a spatula to ensure the liquid settles into all the gaps.
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10
Cover the baking dish tightly with aluminum foil. This traps the steam and ensures the sweet potatoes become perfectly tender.
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11
Bake in the center of the oven for 45 minutes.
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12
Remove the foil. Sprinkle the grated Parmesan cheese evenly over the top.
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13
Return the dish to the oven, uncovered, and bake for an additional 20-25 minutes. The top should be golden brown and the sauce should be bubbling and thickened.
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14
Test for doneness by piercing the center with a knife; it should slide in with zero resistance.
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15
Remove from the oven and let the dish rest for at least 10-15 minutes before serving. This allows the sauce to set so it isn't runny. Garnish with fresh chives and serve.
💡 Chef's Tips
Use a mandoline slicer to get perfectly even potato rounds; uneven slices result in some pieces being mushy while others are crunchy. If the top is browning too quickly after removing the foil, move the rack to a lower position or tent loosely with foil again. For a flavor variation, substitute half of the sweet potatoes with Yukon Gold potatoes for a beautiful color contrast and different starch profile. Always grate your own cheese from a block; pre-shredded cheeses are coated in potato starch which can make your sauce grainy. Make sure to let the dish rest! If you cut into it immediately, the cream sauce will be thin; the rest time is vital for that 'scalloped' texture.
🍽️ Serving Suggestions
Pair this with a herb-crusted roasted pork tenderloin or a classic Thanksgiving turkey. Serve alongside a crisp arugula salad with a lemon vinaigrette to cut through the richness of the cream. Enjoy with a glass of buttery Chardonnay or a dry sparkling cider. This dish works beautifully as a vegetarian main course when served with roasted Brussels sprouts and crusty sourdough bread.