French Caramelized Onion Quiche
French Caramelized Onion Quiche made with puff pastry, slow-cooked onions, eggs, milk, Gruyère cheese, mushrooms, swiss chard, garlic, and thyme. A rich, savory quiche with a flaky crust and creamy filling, perfect for brunch or a light dinner.
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Servings: 6 People
Ingredients
- 1 sheet puff pastry thawed but still cold (if frozen, thaw in the refrigerator for 24 hours)
- 4 tablespoons olive oil divided, plus additional as needed
- 1 large yellow onion halved and thinly sliced
- 1 teaspoon kosher salt divided
- 4 large eggs
- 1 ¼ cups whole milk
- 1 cup grated Gruyère cheese
- 1 tablespoon Dijon mustard
- 2 cloves garlic minced
- 2 cups shiitake mushrooms sliced with stems removed (baby bella mushrooms may be substituted)
- ¼ teaspoon freshly ground black pepper
- 2 cups swiss chard stems removed and sliced into thin ribbons (approximately 1 bunch)
- 1 teaspoon fresh thyme leaves finely chopped
Instructions
Caramelize the Onions
- Heat 2 tablespoons of olive oil in a large skillet over medium heat. Add the sliced onion and ½ teaspoon kosher salt. Cook the onions slowly, stirring occasionally, until they become deeply golden and caramelized, approximately 35–45 minutes.
- If the onions appear dry during cooking, drizzle in additional olive oil as needed. If they begin to brown too quickly, reduce the heat to medium-low to prevent burning.
- Once caramelized, remove the onions from the heat and allow them to cool slightly.
Prepare the Egg Filling
- In a large mixing bowl, whisk together the eggs, whole milk, grated Gruyère cheese, and Dijon mustard until the mixture is smooth and well combined. Set the mixture aside while preparing the remaining vegetables.
Cook the Mushrooms and Greens
- Using the same skillet that was used to cook the onions, add the remaining 2 tablespoons of olive oil over medium heat. Add the minced garlic, sliced mushrooms, black pepper, and the remaining ½ teaspoon kosher salt.
- Sauté the mushrooms, stirring frequently, until they have softened and released their moisture, approximately 2–3 minutes.
- Add the sliced swiss chard to the pan and cook for an additional 1–2 minutes, stirring gently, until the greens have slightly wilted. Remove the skillet from the heat and allow the mixture to cool briefly.
Assemble the Quiche
- Preheat the oven to 400°F (200°C) and lightly grease a pie dish.
- Roll the puff pastry sheet out so that it is slightly larger than the pie dish. Carefully press the pastry into the dish, gently stretching and folding it so it fits evenly. Trim any excess pastry if desired.
- Once the caramelized onions, mushrooms, and swiss chard have cooled slightly, add them to the egg mixture. Stir gently to combine. Add the chopped thyme and mix again until evenly distributed.
- Pour the filling into the prepared pastry crust.
Bake the Quiche
- Place the quiche in the preheated oven and bake uncovered for 35–45 minutes, or until the filling is set and the pastry crust is golden brown.
- If the top begins to brown too quickly during baking, loosely tent the quiche with aluminum foil.
- The center should appear set but retain a slight wobble when removed from the oven. This ensures a silky, creamy texture as the quiche continues to set while resting.
- Allow the quiche to cool for 5–10 minutes before slicing and serving.
Notes
To prepare a gluten-free version of French Caramelized Onion Quiche, substitute the puff pastry with a certified gluten-free pie crust or gluten-free pastry dough.
Ensure that the Dijon mustard and Gruyère cheese used are labeled gluten-free, as some brands may contain additives.
Bake according to the same instructions. The texture of the crust may vary slightly depending on the gluten-free pastry used, but the filling will remain rich, creamy, and flavorful.