Cheesy Sweet Potato Gratin (Printable Version)

Rich gratin with sweet potatoes, caramelized onions, and melted cheese baked until 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 Additions

13 - 1 tbsp all-purpose flour for thickening
14 - 2 tbsp chopped fresh chives for garnish

# Method:

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 - Combine heavy cream, whole milk, dried thyme, ground nutmeg, black pepper, and remaining 1 tbsp butter in a small saucepan. Heat over medium-low until steaming but not boiling. If using flour for thickening, whisk in until smooth.
04 - Arrange half of the sweet potato slices in the prepared baking dish, overlapping slightly. Season lightly with salt.
05 - Spread half of the caramelized onions over the potatoes. Sprinkle with half of the Gruyère and half of the cheddar cheese.
06 - Repeat layering with remaining sweet potatoes, caramelized onions, and remaining cheeses.
07 - Pour the warm cream mixture evenly over the entire layered dish, ensuring it seeps through all layers.
08 - Cover tightly with aluminum foil and 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.
10 - Let gratin rest for 10 minutes before serving to allow layers to set. Garnish with chopped fresh chives if desired.

# Chef's Tips:

01 -
  • The sweetness of the potatoes balances perfectly with savory caramelized onions and two kinds of cheese
  • It comes together surprisingly fast for something that tastes like it took all day
  • Leftovers reheat beautifully and somehow taste even better the next day
02 -
  • Slicing your sweet potatoes too thick means they will not cook through before the cheese burns
  • Not covering the dish for the first bake results in dried out potatoes on top
  • Skimping on the caramelization time for the onions is the biggest mistake you can make
03 -
  • Use a mandoline if you have one for perfectly even potato slices that cook at the same rate
  • Do not rush the onion caramelization step because that deep sweetness is what makes this special

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