Cheesy Sweet Potato Gratin

The first time I made this gratin was for a rainy Sunday dinner when my apartment smelled like nothing but butter and onions for hours. My roommate kept wandering into the kitchen asking if it was done yet. That caramelized onion aroma is basically impossible to resist.

I brought this to a Friendsgiving potluck last year and honestly people kept asking for the recipe. My friend Mark went back for thirds and that is usually a very good sign.

Ingredients

• Sweet potatoes: Thin even slices are crucial here so they cook at the same rate. A mandoline makes this so much easier.
• Yellow onions: Take your time caramelizing them properly. The darker and more golden they get the more flavor they contribute.
• Gruyère and cheddar: Gruyère melts beautifully with that nutty sophistication while sharp cheddar brings the familiar comfort.
• Heavy cream and whole milk: Using both gives you richness without making it too heavy.
• Nutmeg and thyme: These two work surprisingly well together. Nutmeg adds warmth while thyme keeps it grounded.

Instructions

Caramelize the onions:

Melt 2 tablespoons butter in a large skillet over medium heat. Add the sliced onions with a pinch of salt. Stir frequently and let them cook slowly until they are deep golden and smell amazing about 20 to 25 minutes.

Infuse the cream mixture:

While onions are cooking heat the cream milk thyme nutmeg pepper and remaining 1 tablespoon butter in a small saucepan over medium-low heat. Whisk in the flour if you are using it and bring it just to a gentle steam.

Start layering:

Arrange half the sweet potato slices in your prepared baking dish. Give them a light sprinkle of salt. Spread half the caramelized onions on top then add half of both cheeses.

Repeat the layers:

Add the remaining sweet potatoes followed by the rest of the onions and cheeses. Pour the warm cream mixture evenly over everything letting it seep down through the layers.

Bake to perfection:

Cover tightly with foil and bake for 40 minutes. Remove the foil and bake another 20 minutes until the top is bubbly and golden. Let it rest 10 minutes before serving.

Save

This dish has become my go to when I want something that feels fancy but does not require restaurant level technique. Every time I serve it someone says this should be on a menu somewhere.

Make It Your Own

Sometimes I will add a layer of sautéed mushrooms between the potato layers. Earthy mushrooms play so nicely with the sweet potatoes and onions. You could also swap in Monterey Jack for part of the cheese if you want something milder.

Timing Is Everything

You can absolutely make this a day ahead. Just assemble the whole thing cover and refrigerate. Add about 10 minutes to the covered baking time since it will be starting from cold. Letting it sit overnight actually helps the flavors meld together.

Serving Suggestions

A simple green salad with a bright vinaigrette cuts through all that rich creaminess. A crisp white wine like Sauvignon Blanc or a light red like Pinot Noir works beautifully too.

• Let the gratin rest before serving
• Use a sharp knife to test if potatoes are tender
• Sprinkle fresh chives right before serving

Save

There is something deeply satisfying about pulling this bubbling golden dish out of the oven. Hope it brings as much warmth to your table as it has to mine.

Recipe FAQs

→ How are the onions prepared for this dish?

Onions are sliced thin and cooked slowly in butter until deeply golden and caramelized, enhancing their natural sweetness and flavor.

→ Can I use different cheeses in the gratin?

Yes, while Gruyère and sharp cheddar create great flavor, you can substitute similar melting cheeses to suit your taste.

→ What is the purpose of adding nutmeg and thyme?

Nutmeg and thyme add subtle warmth and earthiness, balancing the richness of the cream and cheeses.

→ How do I ensure the sweet potatoes cook evenly?

Slice the sweet potatoes thinly and layer them evenly, seasoning lightly between layers to ensure tenderness throughout baking.

→ Can this dish be prepared ahead of time?

Yes, you can assemble the gratin ahead and refrigerate before baking. Reheat gently to maintain creamy texture.

→ Is this suitable for gluten-free diets?

Yes, if gluten-free flour is used for thickening and cheese labels are checked, this dish can be gluten-free friendly.