Name: Caramelized Onion and Gruyère Tart Recipe
Prep time: 15 min
Cook time: 55 min
Total time: 1 h 10 min
Cuisine: French
Ingredients: 1 sheet puff pastry (thawed); 2 tablespoons olive oil; 2 tablespoons unsalted butter; 3 large yellow onions (thinly sliced); 1/2 teaspoon salt; 1/4 teaspoon black pepper; 1 teaspoon fresh thyme leaves (or 1/2 teaspoon dried); 1 teaspoon balsamic vinegar; 1 1/2 cups grated Gruyère cheese; 1 egg (beaten, for egg wash)

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There’s something irresistible about the marriage of sweet, deeply golden onions and the nutty tang of Gruyère, all nestled atop a flaky, golden pastry. The Caramelized Onion and Gruyère Tart is my go-to dish whenever I want to wow guests or just indulge in a special lunch on a cozy afternoon. Rustic yet impossibly elegant, this tart balances simple ingredients and classic French flavors for a result that feels comforting but gourmet, versatile enough to serve warm for dinner or at room temperature for the most inviting appetizer spread. Once you take your first bite, you’ll be dreaming about sharing (or not sharing!) this delicious creation with your favorite people.

Caramelized Onion and Gruyère Tart Recipe - Recipe Image

Ingredients You’ll Need

You only need a handful of items for this Caramelized Onion and Gruyère Tart, but each one plays a starring role. The magic comes from the way these staples—pastry, cheese, onions, and just a touch of thyme and balsamic—meld together to create something memorable, with contrasting textures and layers of rich, savory flavor.

Puff pastry (1 sheet, thawed): This is your shortcut to a perfectly crisp, buttery crust without the fuss.
Olive oil (2 tablespoons): Adds a hint of fruity flavor and helps soften the onions while they cook.
Unsalted butter (2 tablespoons): Brings richness and depth, making the caramelization process beautifully indulgent.
Yellow onions (3 large, thinly sliced): The sweeter and fresher, the better; they’re the heart of the tart.
Salt (½ teaspoon): Essential for drawing out the onions’ natural sweetness and seasoning every layer.
Black pepper (¼ teaspoon): Just enough to add soft warmth and balance the dish.
Fresh thyme (1 teaspoon, or ½ teaspoon dried): This woodland herb gives the tart a fragrant, French touch.
Balsamic vinegar (1 teaspoon): Just a drizzle brightens the caramelized onions, adding a hint of tanginess.
Gruyère cheese (1½ cups, grated): Nutty, salty, and melty—a showstopper atop the savory tart.
Egg (1, beaten, for egg wash): Helps the pastry’s edges bake up with a beautiful, shiny golden finish.

How to Make Caramelized Onion and Gruyère Tart

Step 1: Prepare the Onions

Start by heating the olive oil and butter in a large skillet over medium heat. Add the sliced onions with a sprinkle of salt and pepper. The real magic happens through patience—let the onions cook slowly for 25 to 30 minutes, stirring every few minutes. As the onions transform into a deep golden brown, their natural sugars will do all the heavy lifting, developing an unforgettable sweetness and rich depth. During the last few minutes, stir in the fresh thyme leaves and a dash of balsamic vinegar. This last step infuses the onions with aroma and brightness. Remove from the heat and allow them to cool slightly while you prep the pastry.

Step 2: Prep the Puff Pastry

On a lightly floured surface, roll out your thawed puff pastry into an even 10×14-inch rectangle. Don’t stress about finding a ruler—just aim for a shape large enough to give every slice a generous bed of onions and cheese. Gently transfer the pastry to a parchment-lined baking sheet. Using a sharp knife, score a ½-inch border around all sides—but don’t cut all the way through. This creates a crisp, puffy edge that looks irresistible once baked. Brush the border with the beaten egg to ensure a golden, glossy finish.

Step 3: Assemble the Tart

Spoon the cooled caramelized onions evenly within the scored border of the puff pastry. It should look like a little bed of glossy, golden onions. Next, sprinkle the Gruyère cheese in a generous, even layer over the onions. You want every bite to melt together with those two stars—a little tangy cheese, a little sweet onion—for perfect flavor harmony.

Step 4: Bake It All Together

Pop the baking sheet into your preheated 400°F (200°C) oven and bake for 20 to 25 minutes. You’ll know your Caramelized Onion and Gruyère Tart is ready when the pastry is puffed and deep gold, and the cheese is bubbly with beautifully toasted spots. It’s hard not to nibble a corner straight from the oven, but do give it a few minutes to cool and set up before slicing—it’ll slice more cleanly and taste even better.

Step 5: Slice and Enjoy

Let the tart cool slightly, then cut it into squares or rectangles using a sharp knife or pizza wheel. The moment you lift a slice, you’ll see those buttery layers and catch the aroma of thyme and onions. Serve warm, or set it out at room temperature if you’re entertaining; either way, don’t be surprised if it disappears quickly!

How to Serve Caramelized Onion and Gruyère Tart

Garnishes

Give your Caramelized Onion and Gruyère Tart a little flair by topping it with a scattering of fresh thyme leaves or a handful of chopped chives. If you want a French bistro touch, a few baby arugula leaves dressed lightly in olive oil add a burst of color and just the right peppery bite.

Side Dishes

This tart truly shines with simple but thoughtful sides. Pair it with a crisp green salad tossed in a lemony vinaigrette, or serve alongside a bowl of homemade tomato soup for satisfying comfort. Even a platter of marinated olives and roasted nuts can make the meal feel special and complete alongside this tart.

Creative Ways to Present

For a party, try cutting the Caramelized Onion and Gruyère Tart into elegant bite-sized squares and arrange on a wooden board for effortless finger food. Hosting brunch? Serve generous slices next to poached eggs and roasted asparagus. You can even offer a bowl of tangy crème fraîche for guests to dollop on top—it’s a simple twist that feels luxe.

Make Ahead and Storage

Storing Leftovers

Wrap any leftover tart in foil or place slices in an airtight container in the fridge. The pastry may lose a hint of its crispness, but the flavors actually deepen, making tomorrow’s lunch almost as exciting as dinner.

Freezing

The Caramelized Onion and Gruyère Tart freezes surprisingly well. Once completely cooled, wrap individual pieces tightly in plastic wrap and foil. Freeze for up to two months. To thaw, simply transfer a piece to the fridge overnight for best results.

Reheating

To recapture that fresh-baked crispness, reheat slices in a 350°F oven for about 10 minutes. Avoid the microwave, which tends to make the pastry soggy. The oven brings back the flakiness and warms the cheese and onions to savory perfection.

FAQs

Can I make the Caramelized Onion and Gruyère Tart ahead of time?

Absolutely! You can caramelize the onions a day in advance and keep them in the refrigerator. Assemble and bake the tart just before serving for the flakiest results.

What if I don’t have Gruyère cheese?

No worries—Swiss, Emmental, or even sharp white cheddar will substitute nicely. Just look for something melty and a bit nutty for the best flavor.

How thinly should I slice the onions?

The thinner the better! Slicing about 1/8 inch thick allows the onions to cook down evenly and develop that delicious, jammy texture essential to the Caramelized Onion and Gruyère Tart.

Can I add extra toppings?

Of course! Cooked bacon, sautéed mushrooms, or even a scattering of roasted garlic all pair beautifully with the base flavors.

Is this tart vegetarian?

Yes, as written, the Caramelized Onion and Gruyère Tart is totally vegetarian. Just be sure your puff pastry doesn’t contain hidden animal fats if cooking for strict vegetarians.

Final Thoughts

The Caramelized Onion and Gruyère Tart is one of those recipes that feels fancy but comes together with surprising ease, making it perfect for gatherings or an elevated weeknight meal. Try it once, and I guarantee it’ll find a permanent spot in your rotation—everyone always asks for the recipe, and I can’t wait for you to taste it for yourself!

Caramelized Onion and Gruyère Tart Recipe

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4.6 from 20 reviews

Author: admin
Total Time: 1 hour 10 minutes
Yield: 6 servings 1x
Diet: Vegetarian

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Description

Indulge in the rich flavors of this Caramelized Onion and Gruyère Tart, a perfect combination of sweet onions and savory cheese on a flaky puff pastry crust.

Ingredients

Scale

Puff Pastry:

1 sheet puff pastry (thawed)

Caramelized Onions:

2 tablespoons olive oil
2 tablespoons unsalted butter
3 large yellow onions (thinly sliced)
1/2 teaspoon salt
1/4 teaspoon black pepper
1 teaspoon fresh thyme leaves (or 1/2 teaspoon dried)
1 teaspoon balsamic vinegar

Additional Ingredients:

1 1/2 cups grated Gruyère cheese
1 egg (beaten, for egg wash)

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Instructions

Preheat the oven: Preheat the oven to 400°F (200°C) and line a baking sheet with parchment paper.
Caramelize the onions: In a skillet, cook the onions with olive oil, butter, salt, and pepper until golden. Add thyme and balsamic vinegar, then cool slightly.
Prepare the pastry: Roll out the puff pastry, score a border, brush with egg wash, and add the caramelized onions and Gruyère.
Bake: Bake for 20–25 minutes until golden and puffed. Slice and serve.