Caramelized Onion Tart
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Flaky pastry, sweet caramelized onions and a creamy egg and Gruyere cheese filling make this onion tart both flavorful and irresistible to serve as an appetizer, dinner or even brunch.
Onion Tart with Gruyere
This caramelized onion tart is a recipe that feels elegant but is just like my Spanish pan con tomate is surprisingly easy to make. With its buttery crust, sweet golden onions, and savory cheese filling, it’s a dish that fills your kitchen with incredible aroma and flavor.
Whether you serve it warm from the oven or at room temperature, it’s a versatile option that works beautifully for brunch, lunch, or a light dinner.
Why You’ll Love This Recipe
- Sweet and savory flavor: The slow-cooked onions turn buttery and sweet which pairs well with the creamy, cheesy filling and flaky crust.
- Versatile and elegant: Ideal for brunch, holidays, or as an appetizer, but simple enough for weeknights.
Ingredient Notes
Find the full recipe with full directions.
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- Onions: I used red onions for their beautiful pop of color, but yellow or sweet onions caramelize just as well and give a mellow, rich sweetness.
- Butter: Adds richness and helps the onions caramelize evenly. You can use olive oil instead if you prefer.
- Eggs: Whisked with cream to create the custard filling that holds everything together.
- Heavy Cream: Provides a silky, creamy texture to the filling. Half-and-half works in a pinch, though the filling will be a little lighter.
- Cheese: Gruyère is the classic choice with its nutty flavor and smooth melt. Parmesan or sharp cheddar are excellent substitutes, or mix a couple together for more depth.
- Nutmeg (optional): A tiny pinch adds warmth and enhances the savory flavor.
- Salt and Pepper: Essential for seasoning and balancing the sweetness of the onions.
- Shortcrust Pastry: A buttery, flaky tart crust made from scratch, or you can save time with store-bought pastry or puff pastry.
How to Make an Onion Tart
Mix flour, butter, and salt until crumbly. Add the egg and water, then knead into a smooth dough.
Chill pastry crust for 30 minutes. Roll out dough, press into a tart pan then prick with a fork then parbake for 10 minutes with pie weights.
Slowly caramelize sliced onions over medium in butter until soft, golden, and sweet (about 20 minutes). Whisk eggs and cream, then stir in cheese, salt, pepper, and nutmeg.
Spread onions evenly in the crust, pour in the cream mixture, and top with more cheese. Cook at 350°F or 25–30 minutes, until the filling is golden and set.
Recipe Tips
- Cook onions low and slow. When making caramelized onions, patience pays off with deep flavor.
- Keep the dough cold for the flakiest crust.
- Don’t overload the crust with onions, spread a thin, even layer to avoid sogginess.
- Always preheat the oven before baking to ensure even cooking and a crisp base.
- Serving suggestions: Pair with a simple green salad for a light lunch, serve at brunch with a fruit salad or enjoy at dinner with a crisp glass of white wine.
More Delicious Recipe to Try
Caramelized Onion Tart
Ingredients
For the crust (shortcut pastry)
- 1 2/3 cups all-purpose flour
- 7 Tablespoons cold unsalted butter , cut into cubes
- 1 large egg
- pinch of salt
- 1-2 Tablespoons cold water
Caramelized onions
- 3-4 large onions (about 1 pound)
- 2 Tablespoons unsalted butter
For the filling
- 1/2 cup heavy cream , preferably 20–30% fat
- 2 large eggs
- 1 cup grated hard cheese , I used Gruyere
- salt and pepper , to taste
- pinch nutmeg , optional
Instructions
Make the crust
- In a large bowl, combine the flour, salt, and butter. Use your fingertips to rub the butter into the flour until the mixture looks like fine breadcrumbs.
- Add the egg and 1 tablespoon of cold water. Mix and knead gently just until the dough comes together, adding an extra splash of water if needed.
- Shape the dough into a ball, wrap it in plastic wrap, and refrigerate for about 30 minutes to rest.
Caramelize the onions
- While the dough chills, peel and thinly slice the onions into half-rings.
- Melt the butter in a large skillet over medium heat. Add the onions and cook, stirring often, until soft and golden brown, about 20 minutes. Keep the heat moderate so they caramelize slowly without burning.
Prepare the Filling
- In a medium bowl, whisk together the eggs and cream until smooth.
- Stir in the grated cheese, a pinch of nutmeg (if using), and season with salt and pepper.
Assemble and bake
- Preheat the oven to 350°F.
- Roll out the chilled dough on a lightly floured surface and fit it into a 9-inch (23 cm) tart pan. Press gently into the edges and trim off any excess. Prick the bottom with a fork.
- Line the crust with parchment paper and fill with pie weights or dried beans. Blind bake for 10 minutes, then carefully remove the parchment and weights.
- Spread the caramelized onions evenly over the crust. Pour the cream and cheese mixture on top.
- Return the tart to the oven and bake for 25–30 minutes, or until the filling is golden and set.
To serve
- Let the tart cool slightly before slicing. It’s delicious served warm, but also just as good at room temperature.
Notes
- Cheese: Parmesan or Cheddar could also be used.
- Onion: I used red onions, but sweet onions or yellow onions can be used as well.
- Store leftovers in an airtight container in the refrigerator for 3-4 days.
Variations
- Add bacon or pancetta: Stir crispy pieces into the onions for extra richness.
- Mini tarts: Bake in smaller tart pans or muffin tins for individual portions. Baking time will most likely be shorter.
- Herbal twist: Top with thyme, rosemary or sage for a different flavor profile.
- Sweet-savory mix: Add a few slices of caramelized pear or apple along with the onions.
FAQs
Make sure the dough rests in the fridge before rolling, and avoid stretching it when fitting it into the pan. This helps the pastry relax and stay in place while baking.
Yes! Caramelized onions can be stored in the fridge for up to 3 days and even taste better as they rest. Reheat them gently before adding to the tart.
Once cooled, store slices in an airtight container in the refrigerator for up to 3 days. Reheat in the oven at 350°F for about 10 minutes to bring back the flaky crust.
Yes. Let the tart cool completely, then wrap it tightly in plastic wrap and foil. Freeze for up to 2 months. To reheat, thaw overnight in the refrigerator and warm in the oven until heated through.
