Cheesy Caramelized Onion Potato Gratin
Cheesy Caramelized Onion Potato Gratin
Ingredients
For the Caramelized Onions and Sauce
- 4 pounds white onions, thinly sliced
- 1 teaspoon salt, plus more to taste
- 6 tablespoons unsalted butter, divided
- 4 garlic, cloves, minced
- 2 teaspoons fresh thyme, chopped, plus more for garnish
- 1/4 cup all-purpose flour
- 1 cup whole milk
- 1 cup heavy cream
- 1/2 teaspoon black pepper, freshly ground, plus more to taste
- 1 teaspoon Dijon mustard
For the Gratin
- 3 pounds potatoes, such as Yukon Gold or Russet, peeled and thinly sliced (about 1/8-inch thick)
- 2 cups hard European cheese, such as Gruyère or Comté, freshly grated, divided
Instructions
- 1
In a large, heavy-bottomed pot or Dutch oven, melt 3 tablespoons of unsalted butter over medium-low heat. Add the thinly sliced white onions and 1 teaspoon of salt. Cook, stirring occasionally, for 30-40 minutes, or until the onions are deeply golden brown, very soft, and significantly reduced in volume. This is the caramelization process.
⏱️ 40 min
- 2
Once the onions are caramelized, add the minced garlic and 1 teaspoon of chopped fresh thyme to the pot. Cook for 1 minute until fragrant.
⏱️ 1 min
- 3
Add the remaining 3 tablespoons of unsalted butter to the pot with the caramelized onions. Once melted, sprinkle in the all-purpose flour. Cook, stirring constantly, for 2-3 minutes to create a roux, ensuring the flour is fully incorporated and lightly toasted.
⏱️ 3 min
- 4
Gradually whisk in the whole milk and heavy cream, a little at a time, until smooth and no lumps remain. Bring the mixture to a gentle simmer, stirring constantly, until the sauce thickens to a creamy consistency, about 5-7 minutes. Remove from heat.
⏱️ 7 min
- 5
Stir in the 1/2 teaspoon of black pepper and the Dijon mustard into the cream sauce. Taste and adjust seasoning with additional salt and pepper if needed.
⏱️ 2 min
- 6
Preheat your oven to 375°F (190°C). Lightly grease a 9x13-inch baking dish.
⏱️ 5 min•🌡️ 375
- 7
Begin layering the gratin: Spread a thin layer of the creamy caramelized onion sauce on the bottom of the prepared baking dish. Arrange a single layer of thinly sliced potatoes over the sauce, slightly overlapping. Sprinkle about 1/2 cup of grated hard European cheese over the potatoes.
⏱️ 5 min
- 8
Repeat the layering process: sauce, potatoes, cheese, until all ingredients are used, ending with a layer of potatoes on top. Ensure the potatoes are evenly distributed.
⏱️ 10 min
- 9
Sprinkle the remaining 1 teaspoon of chopped fresh thyme over the top layer of potatoes. Cover the baking dish tightly with aluminum foil.
⏱️ 1 min
- 10
Bake the covered gratin for 60-75 minutes, or until the potatoes are tender when pierced with a fork. The baking time may vary depending on the thickness of your potato slices.
⏱️ 75 min•🌡️ 375
- 11
Remove the gratin from the oven and carefully remove the foil. Increase the oven temperature to broil (or grill setting). Sprinkle the remaining 1 cup of grated hard European cheese evenly over the top of the gratin.
⏱️ 2 min
- 12
Return the gratin to the oven, uncovered, and broil for 3-5 minutes, watching carefully, until the cheese is melted, bubbly, and golden brown with crispy edges. Be careful not to burn it.
⏱️ 5 min
- 13
Let the gratin rest for 10-15 minutes before serving to allow it to set and make for easier serving. Garnish with additional fresh thyme if desired.
⏱️ 15 min
Kitchen Tools
Nutrition Facts (per serving)
Cheesy Caramelized Onion Potato Gratin
Ingredients
For the Caramelized Onions and Sauce
- 4 pounds white onions, thinly sliced
- 1 teaspoon salt, plus more to taste
- 6 tablespoons unsalted butter, divided
- 4 garlic, cloves, minced
- 2 teaspoons fresh thyme, chopped, plus more for garnish
- 1/4 cup all-purpose flour
- 1 cup whole milk
- 1 cup heavy cream
- 1/2 teaspoon black pepper, freshly ground, plus more to taste
- 1 teaspoon Dijon mustard
For the Gratin
- 3 pounds potatoes, such as Yukon Gold or Russet, peeled and thinly sliced (about 1/8-inch thick)
- 2 cups hard European cheese, such as Gruyère or Comté, freshly grated, divided
Instructions
- 1
In a large, heavy-bottomed pot or Dutch oven, melt 3 tablespoons of unsalted butter over medium-low heat. Add the thinly sliced white onions and 1 teaspoon of salt. Cook, stirring occasionally, for 30-40 minutes, or until the onions are deeply golden brown, very soft, and significantly reduced in volume. This is the caramelization process.
⏱️ 40 min - 2
Once the onions are caramelized, add the minced garlic and 1 teaspoon of chopped fresh thyme to the pot. Cook for 1 minute until fragrant.
⏱️ 1 min - 3
Add the remaining 3 tablespoons of unsalted butter to the pot with the caramelized onions. Once melted, sprinkle in the all-purpose flour. Cook, stirring constantly, for 2-3 minutes to create a roux, ensuring the flour is fully incorporated and lightly toasted.
⏱️ 3 min - 4
Gradually whisk in the whole milk and heavy cream, a little at a time, until smooth and no lumps remain. Bring the mixture to a gentle simmer, stirring constantly, until the sauce thickens to a creamy consistency, about 5-7 minutes. Remove from heat.
⏱️ 7 min - 5
Stir in the 1/2 teaspoon of black pepper and the Dijon mustard into the cream sauce. Taste and adjust seasoning with additional salt and pepper if needed.
⏱️ 2 min - 6
Preheat your oven to 375°F (190°C). Lightly grease a 9x13-inch baking dish.
⏱️ 5 min•🌡️ 375 - 7
Begin layering the gratin: Spread a thin layer of the creamy caramelized onion sauce on the bottom of the prepared baking dish. Arrange a single layer of thinly sliced potatoes over the sauce, slightly overlapping. Sprinkle about 1/2 cup of grated hard European cheese over the potatoes.
⏱️ 5 min - 8
Repeat the layering process: sauce, potatoes, cheese, until all ingredients are used, ending with a layer of potatoes on top. Ensure the potatoes are evenly distributed.
⏱️ 10 min - 9
Sprinkle the remaining 1 teaspoon of chopped fresh thyme over the top layer of potatoes. Cover the baking dish tightly with aluminum foil.
⏱️ 1 min - 10
Bake the covered gratin for 60-75 minutes, or until the potatoes are tender when pierced with a fork. The baking time may vary depending on the thickness of your potato slices.
⏱️ 75 min•🌡️ 375 - 11
Remove the gratin from the oven and carefully remove the foil. Increase the oven temperature to broil (or grill setting). Sprinkle the remaining 1 cup of grated hard European cheese evenly over the top of the gratin.
⏱️ 2 min - 12
Return the gratin to the oven, uncovered, and broil for 3-5 minutes, watching carefully, until the cheese is melted, bubbly, and golden brown with crispy edges. Be careful not to burn it.
⏱️ 5 min - 13
Let the gratin rest for 10-15 minutes before serving to allow it to set and make for easier serving. Garnish with additional fresh thyme if desired.
⏱️ 15 min