Cheesy Sweet Potato Gratin (Printable)
A comforting gratin with layers of sweet potatoes, caramelized onions, and melted cheeses baked golden.
# 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
13 - 1 tbsp gluten-free flour (or all-purpose flour) for thickening
14 - 2 tbsp chopped fresh chives for garnish
# How-To Steps:
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 and a pinch of salt. Cook, stirring frequently, until onions are deeply golden and caramelized, about 20-25 minutes. Add minced garlic and cook for 1 minute more. 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 heat until steaming, do not boil. If using flour, whisk it in until smooth to slightly thicken the mixture.
04 - Arrange half of the sweet potato slices in the prepared baking dish, overlapping slightly. Season lightly with salt. Spread half of the caramelized onions over the potatoes, then sprinkle with half of the Gruyère and cheddar cheese.
05 - Repeat with remaining sweet potato slices, caramelized onions, and cheeses, creating a second complete layer.
06 - Pour the warm cream mixture evenly over the layered ingredients, ensuring it reaches all corners of the dish.
07 - Cover the baking dish tightly with aluminum foil. Bake for 40 minutes to allow potatoes to cook through.
08 - Remove the foil and continue baking uncovered for an additional 20 minutes, or until the top is golden brown and bubbly, and potatoes are fork-tender.
09 - Let the gratin rest for 10 minutes before serving to allow the layers to set. Garnish with fresh chopped chives if desired.
# Expert Tips:
01 -
- The combination of sweet and savory flavors feels like something from a fancy restaurant but comes together surprisingly easily
- It makes beautiful leftovers and actually tastes better the next day as the flavors meld together
02 -
- Slicing the sweet potatoes unevenly will result in some pieces being undercooked while others turn to mush. A mandoline or very sharp knife and patience are your friends here.
- Do not rush the caramelization step. The onions need at least 20 minutes to develop that deep sweet flavor that makes this dish special.
03 -
- Place your baking dish on a rimmed baking sheet to catch any bubbling over in the oven
- The gratin is done when the top is golden and bubbling around the edges but a knife still meets slight resistance in the center