sweet-potato-gratin

Daily Food

Sweet Potato Gratin

Your sweet potatoes are tired of being baked. Give them the chance to become something much more exciting and turn them into sweet potato gratin. Just like the OG potatoes au gratin, these sweet potatoes are layered with plenty of cheese and herby cream sauce and baked until golden brown and bubbly.

Ingredients

  • 3 tbsp. unsalted butter, softened, divided, plus more for foil
  • 4 tsp. cloves garlic, chopped
  • 2 tbsp. chopped fresh thyme leaves, plus more for serving
  • 1 tbsp. chopped fresh sage leaves
  • Kosher salt
  • 1 c. heavy cream
  • 3/4 c. whole milk
  • 1/4 tsp. ground cinnamon
  • 1/4 tsp. ground nutmeg
  • 2 large eggs
  • 3/4 c. grated Parmesan (about 2 oz.), divided
  • Freshly ground black pepper
  • 2 lb. sweet potatoes (mix of purple, orange, and white), peeled and sliced 1/8" thick
  • 2 2/3 c. shredded Gruyère cheese (about 8 1/2 oz.), divided

Directions

  1. Step 1Preheat oven to 375°. Butter a 2-quart casserole or gratin dish with 1 tablespoon butter. In a small saucepan over medium heat, melt 2 tablespoons butter. When butter stops foaming, add garlic and cook, stirring, until fragrant, about 30 seconds. Add thyme, sage, and 1/2 teaspoon salt and cook, stirring occasionally, until heated through, about 30 seconds. Add cream, milk, cinnamon, and nutmeg. Bring to a simmer (do not let boil) and cook, stirring occasionally, until slightly thickened, about 5 minutes. Remove from heat.
  2. Step 2In a medium bowl, beat eggs. Transfer 1 cup cream mixture to a liquid measuring cup or bowl with a spout. Whisking constantly, slowly stream cream mixture into eggs a few tablespoons at a time until incorporated. Add egg mixture to saucepan with remaining cream mixture and whisk until combined. Whisk in 1/2 cup Parmesan. 
  3. Step 3Line bottom of prepared dish with a layer of potatoes, slightly overlapping slices; season with a pinch of salt. Top with 2/3 cup Gruyère and 2/3 cup cream mixture. Repeat 3 times, ending with cream mixture. Top final layer with remaining 1/4 cup Parmesan.
  4. Step 4Butter a piece of foil and tightly cover dish. Bake gratin 30 minutes, uncover, and continue to bake until sides are bubbling and golden brown, about 30 minutes more. Top with thyme.