Cheesy Sweet Potato Gratin (Print View)

Rich gratin featuring sweet potatoes, caramelized onions, and a blend of cheeses baked to 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 Additions

13 - 1 tbsp 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, for 20-25 minutes until deeply golden and caramelized. Add minced garlic during the final minute and remove from heat.
03 - Combine heavy cream, whole milk, thyme, nutmeg, black pepper, and remaining 1 tbsp butter in a small saucepan. Heat over medium-low until steaming but not boiling. If using flour, whisk in until smooth and slightly thickened.
04 - Arrange half the sweet potato slices in the prepared baking dish. Season lightly with salt. Spread half the caramelized onions over potatoes, then sprinkle with half the Gruyère and cheddar cheeses. Repeat layers with remaining potatoes, onions, and cheeses.
05 - Pour the warm cream mixture evenly over the layered ingredients. Cover tightly with aluminum foil and bake for 40 minutes.
06 - Remove foil and continue baking for 20 additional minutes until top is golden brown and potatoes are fork-tender.
07 - Allow gratin to rest for 10 minutes before serving. Garnish with fresh chopped chives if desired.

# Expert Tips:

01 -
  • The combination of Gruyère and sharp cheddar creates this incredible depth that comfort food dreams are made of
  • Caramelized onions add natural sweetness that balances perfectly with the earthy sweet potatoes
  • It looks impressive but comes together with mostly hands-off baking time
02 -
  • Thin, consistent potato slices are non-negotiable, thick pieces will still be crunchy when everything else is perfectly tender
  • Do not rush the onion caramelization step, that brown, jammy texture is what makes this taste like it came from a restaurant kitchen
03 -
  • Use the back of a spoon to gently press down each layer as you build, this eliminates air pockets for even cooking
  • Place your baking dish on a sheet pan in case the cream bubbles over during baking

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