Cheesy Sweet Potato Gratin (Print version)
Layers of sweet potatoes and caramelized onions baked with melted cheeses for a comforting dish.
# 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 or all-purpose flour for thickening
14 - 2 tbsp chopped fresh chives for garnish
# Method:
01 - Preheat your 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 and a pinch of salt. Cook, stirring frequently, until onions are deeply golden and caramelized, about 20-25 minutes. Add minced garlic during the final minute. 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 until steaming but not boiling. If thickening is desired, whisk in flour until smooth.
04 - Arrange half of the sweet potato slices in the prepared baking dish. 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 cheese blend.
06 - Pour the warm cream mixture evenly over the layered ingredients, ensuring the liquid reaches all corners of the dish.
07 - Cover the dish tightly with aluminum foil. Bake for 40 minutes until potatoes begin to soften.
08 - Remove the foil and continue baking for an additional 20 minutes until the top is golden brown and bubbly, and potatoes are fork-tender when pierced.
09 - Let the gratin rest for 10 minutes before serving to allow the layers to set. Garnish with fresh chopped chives if desired.
# Expert advice:
01 -
- The way the natural sweetness of the potatoes plays against the sharp, nutty Gruyère is something I still dream about weeks after making it
- It looks like you spent hours in the kitchen, but most of the cooking time is hands-off while the oven does the work
02 -
- The first time I made this, I rushed the onion caramelization and really regretted it—those 25 minutes are absolutely worth it
- Slicing the potatoes uniformly is key, so if you have a mandoline, this is the perfect time to use it
03 -
- If the top is browning too quickly, tent it loosely with foil while it finishes cooking
- Letting it rest before serving is not optional—it needs those 10 minutes to set properly