Cheesy Sweet Potato Gratin (Printable version)
A comforting baked dish of layered sweet potatoes, caramelized onions, and creamy cheese blend.
# 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 all-purpose flour for thickening
14 - 2 tbsp chopped fresh chives for garnish
# Directions:
01 - Preheat oven to 375°F. Generously grease a 9x13-inch baking dish with butter or cooking spray.
02 - Melt 2 tablespoons butter in a large skillet over medium heat. Add sliced onions and 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 - Combine heavy cream, whole milk, dried thyme, nutmeg, black pepper, and remaining 1 tablespoon butter in a small saucepan. Heat over medium-low until steaming, whisking occasionally. If using flour, whisk in until smooth and slightly thickened. Do not boil.
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 cheeses.
05 - Repeat with remaining sweet potatoes, caramelized onions, and cheeses, creating another complete layer.
06 - Pour the warm cream mixture evenly over the entire dish, ensuring it reaches all corners. Cover tightly with aluminum foil.
07 - Bake covered for 40 minutes, allowing potatoes to steam and soften in the cream.
08 - Remove foil and continue baking uncovered for 20 additional 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 sauce to thicken slightly. Garnish with fresh chives if desired.
# Expert Advice:
01 -
- The caramelized onions create a natural sweetness that balances perfectly with the sharp cheddar
- It’s one of those dishes that tastes even better the next day, if there’s any left
02 -
- Trying to rush the caramelized onions will result in bitter, burnt flavor instead of sweet depth
- The cream mixture should be hot, not boiling, when you pour it over the potatoes
03 -
- A mandoline saves time but use the hand guard because sweet potatoes are dense and slippery
- Season each potato layer lightly with salt rather than dumping it all on top