French Onion Potato Gratin
French Onion Potato Gratin
Ingredients
For the Caramelized Onions
- 2 pounds yellow onions, thinly sliced
- 2 tablespoons unsalted butter
- 1 tablespoon olive oil
- 1 teaspoon granulated sugar
- 1/2 teaspoon salt
- 1/4 teaspoon black pepper, freshly ground
For the Potato Gratin
- 2 1/2 pounds russet potatoes, peeled and thinly sliced (about 1/8 inch thick)
- 3 tablespoons unsalted butter
- 3 tablespoons all-purpose flour
- 2 cups beef broth
- 1 cup heavy cream
- 1 teaspoon fresh thyme, chopped
- 1 teaspoon salt
- 1/2 teaspoon black pepper, freshly ground
- 1/4 teaspoon nutmeg, freshly grated
For the Cheese Topping
- 1 1/2 cups Gruyère cheese, shredded
- 1/2 cup Parmesan cheese, grated
Instructions
- 1
Begin by caramelizing the onions. In a large, heavy-bottomed skillet or Dutch oven, melt 2 tablespoons of unsalted butter and 1 tablespoon of olive oil over medium-low heat. Add the thinly sliced yellow onions, granulated sugar, 1/2 teaspoon of salt, and 1/4 teaspoon of black pepper. Cook slowly, stirring occasionally, for 25-30 minutes, or until the onions are deeply golden brown, very soft, and sweet. Set aside.
⏱️ 30 min
- 2
Preheat your oven to 375°F. Lightly grease a 9x13 inch baking dish with butter.
⏱️ 5 min•🌡️ 375
- 3
Prepare the potatoes by peeling them and slicing them very thinly, about 1/8 inch thick. A mandoline slicer is highly recommended for uniform slices.
⏱️ 10 min
- 4
Prepare the sauce. In a medium saucepan, melt 3 tablespoons of unsalted butter over medium heat. Whisk in the all-purpose flour and cook for 1 minute, stirring constantly, to create a roux.
⏱️ 3 min
- 5
Gradually whisk in the beef broth and heavy cream until the mixture is smooth and lump-free. Bring the sauce to a gentle simmer, then reduce the heat to low. Stir in the chopped fresh thyme, 1 teaspoon of salt, 1/2 teaspoon of black pepper, and 1/4 teaspoon of freshly grated nutmeg. Continue to cook for 2-3 minutes, stirring occasionally, until the sauce has slightly thickened.
⏱️ 5 min
- 6
Assemble the gratin. Arrange about one-third of the thinly sliced potatoes in a single, slightly overlapping layer in the prepared baking dish. Top with half of the caramelized onions. Pour about one-third of the prepared sauce evenly over the onions. Sprinkle with about one-third of the shredded Gruyère cheese.
⏱️ 10 min
- 7
Repeat the layering process: add another one-third of the potatoes, followed by the remaining caramelized onions, another one-third of the sauce, and another one-third of the Gruyère cheese.
⏱️ 5 min
- 8
For the final layer, arrange the remaining potatoes on top. Pour the remaining sauce over the potatoes, ensuring they are mostly covered. Sprinkle with the remaining Gruyère cheese and all of the grated Parmesan cheese.
⏱️ 2 min
- 9
Cover the baking dish tightly with aluminum foil. Bake in the preheated oven for 40 minutes.
⏱️ 40 min•🌡️ 375
- 10
Remove the foil and continue to bake for another 15-20 minutes, or until the potatoes are fork-tender, the sauce is bubbly, and the top is golden brown and crusty.
⏱️ 20 min•🌡️ 375
- 11
Once baked, remove the gratin from the oven and let it rest for 10-15 minutes before serving. This allows the sauce to set and makes for easier serving.
⏱️ 15 min
Kitchen Tools
Nutrition Facts (per serving)
French Onion Potato Gratin
Ingredients
For the Caramelized Onions
- 2 pounds yellow onions, thinly sliced
- 2 tablespoons unsalted butter
- 1 tablespoon olive oil
- 1 teaspoon granulated sugar
- 1/2 teaspoon salt
- 1/4 teaspoon black pepper, freshly ground
For the Potato Gratin
- 2 1/2 pounds russet potatoes, peeled and thinly sliced (about 1/8 inch thick)
- 3 tablespoons unsalted butter
- 3 tablespoons all-purpose flour
- 2 cups beef broth
- 1 cup heavy cream
- 1 teaspoon fresh thyme, chopped
- 1 teaspoon salt
- 1/2 teaspoon black pepper, freshly ground
- 1/4 teaspoon nutmeg, freshly grated
For the Cheese Topping
- 1 1/2 cups Gruyère cheese, shredded
- 1/2 cup Parmesan cheese, grated
Instructions
- 1
Begin by caramelizing the onions. In a large, heavy-bottomed skillet or Dutch oven, melt 2 tablespoons of unsalted butter and 1 tablespoon of olive oil over medium-low heat. Add the thinly sliced yellow onions, granulated sugar, 1/2 teaspoon of salt, and 1/4 teaspoon of black pepper. Cook slowly, stirring occasionally, for 25-30 minutes, or until the onions are deeply golden brown, very soft, and sweet. Set aside.
⏱️ 30 min - 2
Preheat your oven to 375°F. Lightly grease a 9x13 inch baking dish with butter.
⏱️ 5 min•🌡️ 375 - 3
Prepare the potatoes by peeling them and slicing them very thinly, about 1/8 inch thick. A mandoline slicer is highly recommended for uniform slices.
⏱️ 10 min - 4
Prepare the sauce. In a medium saucepan, melt 3 tablespoons of unsalted butter over medium heat. Whisk in the all-purpose flour and cook for 1 minute, stirring constantly, to create a roux.
⏱️ 3 min - 5
Gradually whisk in the beef broth and heavy cream until the mixture is smooth and lump-free. Bring the sauce to a gentle simmer, then reduce the heat to low. Stir in the chopped fresh thyme, 1 teaspoon of salt, 1/2 teaspoon of black pepper, and 1/4 teaspoon of freshly grated nutmeg. Continue to cook for 2-3 minutes, stirring occasionally, until the sauce has slightly thickened.
⏱️ 5 min - 6
Assemble the gratin. Arrange about one-third of the thinly sliced potatoes in a single, slightly overlapping layer in the prepared baking dish. Top with half of the caramelized onions. Pour about one-third of the prepared sauce evenly over the onions. Sprinkle with about one-third of the shredded Gruyère cheese.
⏱️ 10 min - 7
Repeat the layering process: add another one-third of the potatoes, followed by the remaining caramelized onions, another one-third of the sauce, and another one-third of the Gruyère cheese.
⏱️ 5 min - 8
For the final layer, arrange the remaining potatoes on top. Pour the remaining sauce over the potatoes, ensuring they are mostly covered. Sprinkle with the remaining Gruyère cheese and all of the grated Parmesan cheese.
⏱️ 2 min - 9
Cover the baking dish tightly with aluminum foil. Bake in the preheated oven for 40 minutes.
⏱️ 40 min•🌡️ 375 - 10
Remove the foil and continue to bake for another 15-20 minutes, or until the potatoes are fork-tender, the sauce is bubbly, and the top is golden brown and crusty.
⏱️ 20 min•🌡️ 375 - 11
Once baked, remove the gratin from the oven and let it rest for 10-15 minutes before serving. This allows the sauce to set and makes for easier serving.
⏱️ 15 min