Cheesy Sweet Potato Gratin (Printable Version)

Rich gratin layered with sweet potatoes, caramelized onions, and a blend of cheeses baked until golden.

# What You 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

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

# How to Make It:

01 - Preheat oven to 375°F. Grease a 9x13-inch baking dish with butter or cooking spray.
02 - Melt 2 tbsp butter in a large skillet over medium heat. Add sliced onions with a pinch of salt. Cook, stirring frequently, until deeply golden and caramelized, about 20-25 minutes. Add minced garlic during the last minute and remove from heat.
03 - In a small saucepan, combine heavy cream, whole milk, dried thyme, ground nutmeg, black pepper, and remaining 1 tbsp butter. Heat over medium-low until steaming but not boiling. If thickening is desired, whisk in flour until smooth.
04 - Arrange half of the sweet potato slices in the prepared baking dish. Season lightly with salt, then spread half of the caramelized onions over the potatoes. Sprinkle with half of the Gruyère and cheddar cheese.
05 - Repeat layering with remaining sweet potatoes, caramelized onions, and cheese blend.
06 - Pour the warm cream mixture evenly over the layered ingredients, ensuring coverage across the entire dish.
07 - Cover baking dish tightly with aluminum foil. Bake for 40 minutes to allow potatoes to cook through.
08 - Remove foil and continue baking uncovered for 20 minutes, until top is golden brown and potatoes are fork-tender.
09 - Allow gratin to rest for 10 minutes before serving. Garnish with fresh chives if desired.

# Expert Advice:

01 -
  • The way the sweet potatoes become meltingly tender while holding their shape is pure comfort food magic
  • Caramelized onions add a savory depth that balances the natural sweetness perfectly
  • That moment when you pull off the foil and the cheese has turned into a golden crust is worth the wait
02 -
  • Slicing your sweet potatoes unevenly will result in some pieces undercooked while others turn to mush
  • Skipping the foil-covered baking phase means the potatoes will not cook through before the cheese burns
  • Rushing the caramelization process yields bland onions instead of the deep, sweet flavor this dish deserves
03 -
  • Use a mandoline if you have one—it saves time and guarantees perfectly even slices
  • Grate your own cheese instead of buying pre-shredded for a smoother melt
  • Let the cream mixture cool slightly before pouring so it does not cook the potato edges

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