Cheesy Sweet Potato Gratin

The kitchen smelled like sweet earth and butter, sunlight streaming through the window as I wrestled with a mandoline and a mountain of sweet potatoes. My roommate kept poking her head in, asking if it was ready yet, the onions slowly turning into something golden and patient on the stove.

I first made this for a rainy Sunday dinner with friends, skeptical that something so simple could impress. But when everyone went silent for a full minute after the first bite, I knew this recipe was staying in my regular rotation forever.

Ingredients

• Sweet potatoes: Thin, even slices are crucial here—take your time with the knife or treat yourself to a mandoline for uniform layers
• Yellow onions: The long, slow caramelization is what transforms them from simple to extraordinary—do not rush this step
• Gruyère and sharp cheddar: The Gruyère brings that nutty, sophisticated melt while cheddar punches up the flavor
• Heavy cream and whole milk: The combination creates the perfect velvety consistency without being overwhelmingly rich
• Thyme and nutmeg: Warm, aromatic spices that complement the natural sweetness of the potatoes
• Butter: Three tablespoons might seem generous, but it is what creates that luscious, silky mouthfeel
• Garlic: Added at the very end of caramelization so it mellows without burning
• Chives: Fresh green sprinkles on top cut through all that richness with a bright, oniony finish

Instructions

Caramelize the onions:

Melt 2 tablespoons butter in a large skillet over medium heat, add sliced onions with a pinch of salt, and let them cook slowly, stirring often, until they turn deep golden and smell incredibly sweet—about 20 to 25 minutes

Add the garlic:

Stir in the minced garlic during the last minute of cooking so it softens and releases its aroma without turning bitter

Warm the cream mixture:

In a small saucepan, gently heat the cream, milk, thyme, nutmeg, black pepper, and remaining butter until steaming, whisking in the flour if you want a slightly thicker sauce

Start layering:

Arrange half the sweet potato slices in your greased baking dish, sprinkle them lightly with salt, then spread half the caramelized onions over the top

Add the cheese:

Sprinkle half of both cheeses over the onions, creating little pockets of melting goodness throughout the layers

Repeat the layers:

Add the remaining sweet potatoes, onions, and cheese, building upward like a delicious edible tower

Pour over the cream:

Slowly drizzle the warm cream mixture over everything, letting it seep down through all the layers

Cover and bake:

Tent the dish tightly with foil and bake for 40 minutes so the potatoes steam and tenderize in their own bath

Uncover and brown:

Remove the foil and bake for another 20 minutes until the top is bubbly, golden, and absolutely irresistible

Rest before serving:

Let the gratin sit for 10 minutes so the creamy sauce sets up slightly and makes serving much easier

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This recipe has become my go-to for holiday dinners because it somehow feels fancy enough for company but cozy enough for a Tuesday night. Last Thanksgiving, my cousin who claims to hate sweet potatoes went back for thirds.

Make It Your Own

Sometimes I sprinkle smoked paprika between layers for a subtle smoky undertone that plays beautifully with the sweet and savory elements. Sautéed mushrooms make an earthy addition, while a handful of baby spinach wilts nicely between layers for some color.

The Make-Ahead Magic

You can assemble the entire gratin up to a day before baking, covering it tightly and storing it in the refrigerator. Let it come to room temperature for about 30 minutes before baking, adding a few extra minutes to the covered baking time if needed.

Perfect Pairings

A crisp Sauvignon Blanc cuts through the richness while a light Pinot Noir complements the caramelized notes. For a complete meal, serve alongside roasted chicken or pork tenderloin.

• A simple green salad with vinaigrette balances the creaminess
• Crusty bread is perfect for mopping up any extra sauce
• Roasted Brussels sprouts add a nice bitter contrast to the sweet potatoes

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There is something deeply satisfying about serving a dish that looks this impressive but comes together with such simple ingredients.

Common Questions

→ How do I caramelize onions properly?

Cook sliced onions slowly over medium heat with butter and a pinch of salt, stirring frequently until golden brown and sweet, about 20-25 minutes.

→ Can I make this dish gluten-free?

Yes, by using gluten-free flour for thickening and ensuring cheeses have no gluten additives, the dish remains gluten-free.

→ What cheeses work best for this gratin?

Gruyère and sharp cheddar provide a rich, creamy texture and balanced flavor that melts beautifully in the gratin.

→ How do I achieve a golden crust on top?

Bake covered initially to cook through, then uncover and bake longer to allow the top to turn golden brown and slightly crisp.

→ Can this dish be prepared in advance?

Yes, it can be assembled ahead and gently reheated before serving without losing its creamy texture and flavor.

→ What seasoning enhances the gratin?

Dried thyme, ground black pepper, nutmeg, and salt combine to add warm and savory depth to the creamy layers.