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Comforting Scalloped Potatoes au Gratin Recipe Easy Best with Gruyère and Caramelized Onions

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A cozy and indulgent side dish featuring thinly sliced Yukon Gold potatoes layered with caramelized onions and a creamy Gruyère cheese sauce, baked to golden perfection.

Ingredients

Scale
  • 2 pounds Yukon Gold potatoes, peeled and thinly sliced
  • 2 large yellow onions, thinly sliced
  • 2 tablespoons unsalted butter (for sautéing the onions)
  • 1 teaspoon kosher salt
  • ½ teaspoon freshly ground black pepper
  • 3 tablespoons unsalted butter (for cheese sauce)
  • 3 tablespoons all-purpose flour (use gluten-free flour if needed)
  • 2 cups whole milk, warmed
  • 1 ½ cups grated Gruyère cheese
  • ¼ teaspoon ground nutmeg
  • ½ cup grated Parmesan cheese (for topping)

Instructions

  1. Caramelize the Onions: Heat 2 tablespoons of butter in a large skillet over medium-low heat. Add the thinly sliced onions, sprinkle with a pinch of salt, and cook slowly, stirring every few minutes, until golden brown and sweet, about 30 to 40 minutes. Add a splash of water if onions start sticking or drying out.
  2. Prepare the Potatoes: Peel and slice the potatoes into ⅛-inch (3 mm) thick rounds. Rinse slices in cold water to remove excess starch, then dry thoroughly with a clean towel.
  3. Make the Cheese Sauce: In a medium saucepan, melt 3 tablespoons of butter over medium heat. Whisk in the flour and cook for 1-2 minutes until smooth and nutty. Gradually whisk in warmed milk, stirring constantly until sauce thickens, about 5-7 minutes. Remove from heat and stir in grated Gruyère cheese, nutmeg, salt, and pepper until melted and smooth.
  4. Assemble the Dish: Preheat oven to 350°F (175°C). Butter a 9×13-inch baking dish. Layer half the potato slices evenly, sprinkle with half the caramelized onions, and pour half the cheese sauce over. Repeat layers. Sprinkle grated Parmesan cheese evenly on top.
  5. Bake: Cover dish tightly with foil and bake for 45 minutes. Remove foil and bake an additional 20-25 minutes until top is golden and bubbly and potatoes are tender. Let rest for 10 minutes before serving.

Notes

Caramelize onions slowly over low heat for best sweetness. Slice potatoes evenly to ensure uniform cooking. Warm milk before adding to roux to avoid lumps. Let casserole rest after baking to set sauce. Tent with foil if top browns too quickly; broil last 2-3 minutes for crustier top.

Nutrition

Keywords: scalloped potatoes, au gratin, Gruyère cheese, caramelized onions, comfort food, easy side dish, cheesy potatoes

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