Cheesy Sweet Potato Gratin (Printable)
Layers of sweet potatoes, caramelized onions, and cheeses baked to a golden, tender finish.
# Ingredient List:
→ 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 flour for thickening
14 - 2 tbsp chopped fresh chives for garnish
# Steps:
01 - Preheat oven to 375°F. Grease a 9x13-inch baking dish with butter or cooking spray.
02 - In a large skillet over medium heat, melt 2 tbsp butter. 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 final minute and remove from heat.
03 - In a small saucepan, combine heavy cream, whole milk, dried thyme, nutmeg, black pepper, and remaining 1 tbsp butter. Heat over medium-low heat until steaming but not boiling. If using flour for thickening, whisk in until smooth and slightly thickened.
04 - Arrange half of the sweet potato slices in the prepared baking dish. Season lightly with salt.
05 - Spread half of the caramelized onions over the potatoes. Sprinkle evenly with half of the Gruyère and half of the cheddar cheese.
06 - Repeat layers with remaining sweet potato slices, caramelized onions, and cheeses.
07 - Pour the warm cream mixture evenly over the layered ingredients, ensuring it reaches all corners of the dish.
08 - Cover the dish tightly with aluminum foil. Bake for 40 minutes until potatoes begin to soften.
09 - Remove foil and continue baking for 20 minutes until the top is golden brown and bubbly, and potatoes are fork-tender when pierced.
10 - Let the gratin rest for 10 minutes before serving to allow layers to set. Garnish with chopped fresh chives if desired.
# Expert Advice:
01 -
- The combination of sweet potatoes and caramelized onions creates this incredible depth of flavor that feels fancy but comes together so easily
- Unlike traditional potato gratins, this version brings natural sweetness that balances perfectly with the rich, creamy cheese sauce
02 -
- I once rushed the onion caramelization step and the gratin just wasnt the same, so give those onions the full 20-25 minutes to develop that deep sweetness
- Covering the dish for the first 40 minutes is crucial or the top will burn before the potatoes in the middle are cooked through
03 -
- Use a mandoline if you have one to get perfectly even potato slices that cook at the same rate
- The gratin is done when a knife slides through the potatoes with no resistance and the cheese is bubbling eagerly around the edges