Extra Cheesy Sweet Potato Gratin: The Perfect Side Dish

This cheesy sweet potato gratin is the perfect side dish for any meal or gathering! The cheese and cream make it extra savory and decadent while the sweet potatoes add a hint of sweetness.

  • Author: Bri McKoy


  • 2 lbs sweet potatoes, peeled and thinly sliced (about 1/8 inch thickness)
  • 2 TBS butter, divided
  • 1 TBS olive oil
  • 1 yellow onion, chopped
  • 1/2 TBS fresh thyme
  • 1 tsp rosemary
  • 1 tsp salt
  • 1/4 tsp pepper
  • 1 cup heavy cream
  • 1 cup (5 ounces or .30 lbs) gruyere or fontina cheese, shredded
  • 1 cup parmesan cheese, shredded and divided


  1. Preheat oven to 400 degrees.
  2. Peel and then thinly slice sweet potatoes. To get an even thin slice use a mandoline or slice with a sharp knife. Should be about 1/8 inch thick.
  3. In a sauce pan add 1 TBS butter and olive oil. Once the butter is melted add the onion, thyme, rosemary, salt and pepper. Saute until the onion is soft, about 3-5 minutes. Set aside.
  4. In a sauce pot, add the heavy cream and 1 TBS of butter. Bring to a simmer on medium high heat. Once bubbling, remove from burner and set aside.
  5. In a baking dish, add a layer of the sweet potatoes (it is ok if the potatoes slightly overlap each other). Then add the onion mixture. Then add some of the gruyere and parmesan cheese (only use 1/2 cup of the parmesan for the layering, reserve the other 1/2 cup for the top layer). Repeat with another layer of sweet potatoes, onion mixture and cheese until all ingredients are used. The last item should be the onion mixture (do not add a top layer of cheese).
  6. Slowly pour the heavy cream sauce over the whole dish of sweet potatoes.
  7. Bake for 40 minutes.
  8. After 40 minutes, remove the baking dish from the oven. Set the oven to broil. Sprinkle the remaining 1/2 cup parmesan cheese on top of the sweet potatoes and return to oven. Bake until cheese is melty and bubbly – about 5-10 more minutes.
  9. Allow to sit for 10-20 minutes so the juices will settle and thicken. Serve!


Can be assembled up to two days ahead of time. Place an airtight lid over dish and refrigerator until ready to bake.