Serves 12


  • 1 Tbsp. extra-virgin olive oil, plus more for greasing pan
  • 2 garlic cloves, finely chopped
  • 1 medium sweet onion, chopped
  • 2 cups heavy cream
  • 1/2 cup unsweetened pumpkin puree
  • 2 Tbsp. whole grain mustard
  • 1 Tbsp. herbes de Provence, without lavender
  • 1 Tbsp. kosher salt, divided
  • 1/2 tsp. ground black pepper
  • 4 slices thick-cut bacon, sliced into 1/4" pieces
  • 2 1/2 pounds russet potatoes (3 or 4 medium potatoes), peeled and cut into 1/8"-thick slices, preferably with a mandoline
  • 2 1/2 pounds sweet potatoes or yams (3 or 4 medium potatoes or yams), peeled and cut into 1/8"-thick slices, preferably with a mandoline
  • 1/2 cup all-purpose flour
  • 1/2 cups grated Gruyère (6 ounces), divided
  • 1/2 cup chopped hazelnuts


    Active time: 1 hour
    Total time: 2½ to 3 hours

    Preheat oven to 350°. Lightly oil a 9" x 13" casserole dish and set aside. In a medium pot, heat oil, add garlic and onion, and cook, stirring often, until just tender, about 5 minutes. Whisk in cream, pumpkin, mustard, herbes de Provence, 1 1/2 tsp. salt and pepper, and cook 5 minutes more. Meanwhile, in a large skillet, cook bacon over medium heat, stirring occasionally, until just crisp, 8 to 10 minutes. Using a slotted spoon, transfer bacon to a paper towel–lined plate, then pour the remaining fat in the skillet into the cream mixture, whisking to combine. Set aside.

    In a large bowl, use your hands to toss together potatoes, flour and remaining 1 1/2 tsp. salt until coated. Fold in reserved cream mixture and 1 cup Gruyère. Transfer to prepared dish, arranging potatoes in flat layers and pressing down gently to fit.

    Lightly oil a large piece of foil and use it to snugly cover dish. Arrange dish on a foil-lined rimmed baking sheet to catch any drips and bake until just tender when pierced in the center with a paring knife, about 1 hour 15 minutes. Uncover; sprinkle with hazelnuts, reserved bacon and remaining 1/2 cup Gruyère; and bake until cheese is golden and bubbly and liquid has thickened, about 30 minutes. Let rest at least 15 minutes before serving.

    Make ahead: Recipe can be made up to 4 days in advance. To reheat: Preheat oven to 325°. Place casserole dish in a larger pan and add boiling water to fill halfway up the outside of the dish. Cover gratin with aluminum foil and bake for 30 to 45 minutes.

    Next Story