Apple and Sweet Potato Gratin

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Creamy and flavored with fresh thyme, this delicious side dish gets additional sweetness and texture from crisp apples.

Apple and Sweet Potato Gratin
 
Ingredients
  • 1 tablespoon vegetable oil
  • 2½ cups chopped yellow onion
  • ¾ teaspoon kosher salt, divided
  • 2 tablespoons water
  • 4½ cups (⅛-inch-thick) sliced peeled sweet potatoes
  • 2 cups (¼-inch-thick) sliced Gala apples (about 2 medium apples)
  • 2 cups (¼-inch-thick) sliced Granny Smith apples (about 2 medium apples)
  • 1⅓ cups shredded fontina cheese, divided
  • 3 teaspoons chopped fresh thyme, divided
  • ¾ teaspoon ground black pepper, divided
  • ⅓ cup heavy whipping cream
  • 1 tablespoon unsalted butter, cubed
  • ¼ cup panko (Japanese bread crumbs)
  • Garnish: chopped fresh thyme
Instructions
  1. Preheat oven to 375°.
  2. In a 12-inch cast-iron skillet, heat oil over medium-high heat. Reduce heat to medium. Add onion; cook until lightly browned, about 4 minutes. Reduce heat to medium-low; stir in ¼ teaspoon salt. Cover and cook, stirring occasionally, until tender, about 25 minutes. Add 2 tablespoons water, 1 tablespoon at a time, to prevent onion from sticking to pan, if necessary. Remove onion from pan.
  3. In skillet, arrange one-third each of sweet potatoes, apples, and onions in a single layer. Sprinkle with ⅓ cup cheese, 1 teaspoon thyme, ¼ teaspoon pepper, and ⅛ teaspoon salt. Repeat layers once. Top with remaining sweet potatoes, apples, and onions, ⅛ teaspoon salt, remaining 1 teaspoon thyme, and remaining ¼ teaspoon pepper. Pour cream onto layers. Dot with butter. Cover with foil.
  4. Bake until potatoes are tender, about 45 minutes. Uncover and sprinkle with bread crumbs, remaining ⅔ cup cheese, and remaining ⅛ teaspoon salt. Bake until cheese is melted, about 8 minutes more. Let stand for 15 minutes before serving. Garnish with thyme, if desired.