Cheesy Sweet Potato Gratin (Printable)

Rich layers of sweet potatoes, caramelized onions, and melted cheeses baked until golden and tender.

# What You’ll Need:

→ Vegetables

01 - 2 lbs sweet potatoes, peeled and thinly sliced
02 - 2 large yellow onions, thinly sliced
03 - 2 cloves garlic, minced

→ Dairy & Cheese

04 - 2 cups shredded Gruyère cheese
05 - 1 cup shredded sharp cheddar cheese
06 - 1 1/2 cups heavy cream
07 - 1/2 cup whole milk
08 - 3 tbsp unsalted butter

→ Seasonings

09 - 1/2 tsp dried thyme
10 - 1/2 tsp ground black pepper
11 - 1/2 tsp salt plus more to taste
12 - 1/4 tsp ground nutmeg

→ Optional Additions

13 - 1 tbsp gluten-free or all-purpose flour for thickening
14 - 2 tbsp chopped fresh chives for garnish

# How To Make It:

01 - Preheat oven to 375°F. Generously grease a 9x13-inch baking dish with butter or cooking spray.
02 - Melt 2 tablespoons butter in a large skillet over medium heat. Add sliced onions with a pinch of salt. Cook, stirring frequently, for 20-25 minutes until deeply golden and caramelized. Add minced garlic during the final minute.
03 - In a small saucepan, combine heavy cream, whole milk, thyme, nutmeg, black pepper, and remaining 1 tablespoon butter. Heat over medium-low until steaming, not boiling. If using flour, whisk until smooth and slightly thickened.
04 - Arrange half the sweet potato slices in the prepared dish. Season lightly with salt. Spread half the caramelized onions over potatoes, then sprinkle with half the Gruyère and cheddar.
05 - Repeat with remaining sweet potatoes, caramelized onions, and cheese blend. Pour the warm cream mixture evenly over all layers.
06 - Cover dish tightly with aluminum foil. Bake for 40 minutes to steam and soften potatoes.
07 - Remove foil and continue baking uncovered for 20 minutes until top is golden brown and potatoes are fork-tender.
08 - Let gratin rest for 10 minutes before serving to set. Garnish with fresh chives if desired.

# Expert Tips:

01 -
  • The caramelized onions create a natural sweetness that balances perfectly with the sharp cheeses
  • This dish looks stunning coming out of the oven but is surprisingly straightforward to make
  • Leftovers reheat beautifully for lunch the next day, if they even last that long
02 -
  • Dont rush the onion caramelization because those deep, sweet flavors are what make this dish special
  • Use a mandoline if you have one since uniformly thin potatoes ensure even cooking
  • The gratin should jiggle slightly when it comes out of the oven but will firm up as it rests
03 -
  • If the top starts browning too quickly, tent it loosely with foil for the last 10 minutes
  • Try adding a layer of sautéed mushrooms between the potato layers for extra umami
  • Leftovers reheat wonderfully in a 350°F oven for about 20 minutes

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