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–+ servings

French Onion Potatoes au Gratin

These rich and creamy potatoes are layered with caramelized onions and plenty of cheese!
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Prep Time 30 minutes
Total Time 2 hours 45 minutes
Course Side Dish
Cuisine French
Servings 10 Yield
Calories 547 kcal

Ingredients
  

  • 4 Tbsp. salted butter, plus more for the baking dish
  • 2 Tbsp. olive oil
  • 5 onions, thinly sliced
  • 1 1/2 tsp. kosher salt
  • Black pepper, to taste
  • 1 tsp. sugar
  • 1 Tbsp. fresh thyme, chopped
  • 1/4 cup dry sherry
  • 1/2 cup low-sodium beef broth
  • 2 Tbsp. all-purpose flour
  • 1 1/2 cups heavy cream
  • 1 1/2 cups whole milk 
  • 1/4 tsp. freshly grated nutmeg
  • 6 oz. gruyere cheese, shredded
  • 6 oz. swiss cheese, shredded
  • 5 large russet potatoes, peeled, halved and sliced 1/4 inch thick
  • 1/4 cup grated parmesan cheese
  • Chopped fresh chives, for topping

Instructions
 

  • Preheat the oven to 375˚. Butter a 9-by-13-inch baking dish. Heat the olive oil and 2 tablespoons butter in a large skillet over medium-low heat. Add the onions, 1 teaspoon salt, a few grinds of pepper and the sugar. Stir, then cover and cook, stirring once, 10 minutes. Uncover, increase the heat to medium and cook, stirring, 10 more minutes. Add the thyme, sherry and broth. Cook, stirring, until the liquid evaporates and the onions are caramelized, about 15 more minutes. 
  • Melt the remaining 2 tablespoons butter in a dutch oven over medium heat. Stir in the flour and cook 1 minute, then whisk in the heavy cream and milk. Add the remaining ½ teaspoon salt and the nutmeg. Bring to a simmer, whisking until smooth. Cook, stirring, until thickened, 2 to 3 minutes. Remove from the heat. Stir in all but ½ cup each of the gruyère and Swiss until melted. Stir in the potatoes. 
  • Layer half of the potatoes in the baking dish, then half of the onions. Repeat with the remaining potatoes and onions. Sprinkle with the reserved gruyère and Swiss and the parmesan. Cover with foil, tenting it so it doesn’t touch the cheese; bake until the potatoes are tender, 45 to 55 minutes. Uncover and bake until golden brown, 20 to 25 minutes. Let sit 20 minutes before serving. Top with chives.

Nutrition

Calories: 547kcalCarbohydrates: 41gProtein: 18gFat: 33gSaturated Fat: 19gTrans Fat: 1gCholesterol: 93mgSodium: 578mgPotassium: 1017mgFiber: 4gSugar: 7gCalcium: 479mgIron: 2mg
Keyword French Onion Potatoes au Gratin
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