Cheesy Sweet Potato Gratin (Printable Version)

Layers of sweet potatoes and caramelized onions topped with melted cheeses and creamy sauce.

# 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 and cook 1 minute more.
03 - In a small saucepan, combine heavy cream, whole milk, dried thyme, nutmeg, black pepper, and remaining 1 tbsp butter. 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.
05 - Spread half the caramelized onions over the potatoes. Sprinkle with half the Gruyère and half the cheddar cheese.
06 - Repeat with remaining sweet potatoes, caramelized onions, and cheeses.
07 - Pour the warm cream mixture evenly over the entire dish, ensuring it penetrates the layers.
08 - Cover tightly with aluminum foil. Bake for 40 minutes.
09 - Remove foil and continue baking uncovered for 20 minutes until top is golden brown and potatoes are fork-tender.
10 - Let gratin rest for 10 minutes before serving. Garnish with fresh chives if desired.

# Expert Tips:

01 -
  • The sweet and savory combo hits every comfort button you have
  • It looks impressive but practically cooks itself
  • Leftovers reheat beautifully for breakfast the next day
02 -
  • Do not rush caramelizing the onions, that 20 minute wait is what builds the complex flavor base
  • Let the cream mixture cool slightly before pouring so it does not curdle on contact
  • The resting period is non negotiable unless you want a soupy mess instead of neat slices
03 -
  • Slice your potatoes as uniformly as possible, they cook at the same rate and look stunning
  • Season each layer lightly rather than dumping all the salt at the end
  • Use the fork test, if it slides through potatoes with no resistance, it is done

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