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French Onion Potatoes

French onion potatoes layer thin Yukon Gold potatoes with deeply golden onions, a creamy beef broth sauce, and bubbling Gruyère. Baked until tender and browned, this casserole brings the flavor of French onion soup to a hearty potato side dish.
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Prep Time 20 minutes
Cook Time 1 hour 39 minutes
Resting 15 minutes
Total Time 2 hours 14 minutes
Servings: 8 servings
Course: Side Dish
Cuisine: French
Calories: 450
Ingredients Equipment Method Notes

Ingredients
  

Onion sauce
  • 2 tbsp unsalted butter
  • 2 yellow onions large, about 1 1/2 pounds, thinly sliced
  • 0.5 tsp kosher salt
  • 2 cloves garlic minced
  • 2 tbsp all-purpose flour
  • 1.5 cup low-sodium beef broth
  • 1.5 cup heavy cream
  • 1 tsp dried thyme
Potatoes
  • 1 tsp canola oil for greasing
  • 2.5 lb Yukon Gold potatoes sliced 1/8 inch thick
  • 1 tsp kosher salt
  • 0.25 tsp ground black pepper
Cheese topping
  • 8 oz Gruyère cheese shredded

Equipment

  • 1 12-inch skillet
  • 1 9x13-inch baking dish

Method
 

Make the onion sauce
  1. Heat the oven to 375°F.
  2. Melt the butter in a 12-inch skillet over medium heat.
  3. Add the onions and 1/2 teaspoon salt and cook, stirring often, for 25–30 minutes, until very soft and deep golden.
  4. Stir in the garlic and cook for 30 seconds.
  5. Sprinkle in the flour and cook, stirring, for 1 minute.
  6. Gradually whisk in the beef broth, then the heavy cream and thyme.
  7. Bring the sauce to a gentle simmer and cook for 2–3 minutes, whisking, until lightly thickened.
Assemble the potatoes
  1. Brush the bottom and sides of a 9x13-inch baking dish with the canola oil.
  2. Arrange half the potatoes in overlapping layers, sprinkle with half the remaining salt and pepper, and spoon over half the onion sauce.
  3. Repeat with the remaining potatoes, seasoning, and sauce.
  4. Cover the dish tightly with foil and bake for 45–55 minutes, until a paring knife meets only slight resistance when inserted into the center.
Add the cheese topping and bake
  1. Remove the foil and scatter the Gruyère evenly over the potatoes.
  2. Bake uncovered for 15–20 minutes, until the cheese is bubbling and browned and a knife slides easily through the potatoes.
  3. Let the potatoes rest for 15 minutes before serving.

Notes

Slice the potatoes evenly so they cook at the same rate. Refrigerate leftovers for 3–4 days; freezing is not recommended because the cream sauce may change texture. For a gluten-free option, use a gluten-free all-purpose flour blend.