Name: french onion tart Recipe
Prep time: 20 min
Cook time: 55 min
Total time: 1 h 15 min
Cuisine: French
Ingredients: 1 sheet pre-made puff pastry (Around 10 oz or 280 g); 4 medium onions (Approximately 2 lbs or 900 g, thinly sliced); 2 tablespoons olive oil; 1 tablespoon butter; 1 teaspoon sugar; 1 teaspoon salt; 1 teaspoon black pepper; 1 teaspoon fresh thyme leaves (Or ½ teaspoon dried thyme); 1 cup Gruyère cheese, grated (Approximately 100 g); 2 large eggs; 1 cup heavy cream (Approximately 240 ml)

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If you have a soft spot for rich, savory flavors wrapped in buttery, flaky goodness, this french onion tart is about to become your new favorite. Imagine caramelized onions mingling with melted Gruyère cheese, nestled inside a golden puff pastry crust that’s crisp on the edges and tender in all the right places. Every bite offers a perfect balance of sweet, salty, and creamy textures that feel both indulgent and wonderfully comforting. Whether it’s for a casual brunch, a light dinner, or a special gathering, this french onion tart will impress while feeling effortlessly elegant.

Ingredients You’ll Need

The beauty of this french onion tart lies in its simple but thoughtfully chosen ingredients. Each element plays a crucial role—from the sweetness of caramelized onions to the slight tanginess of Gruyère and the luxurious custard that ties it all together.

Puff pastry sheet: Provides a flaky, buttery foundation that crisps beautifully when baked.
Onions (4 medium): Thinly sliced for perfect caramelization and sweetness.
Olive oil (2 tablespoons): Adds a subtle fruitiness and helps gently cook the onions.
Butter (1 tablespoon): Enhances richness and assists in caramelization.
Sugar (1 teaspoon): Helps bring out the natural sweetness of the onions.
Salt (1 teaspoon): Balances all the flavors perfectly.
Black pepper (1 teaspoon): Adds a gentle kick and warmth.
Fresh thyme leaves (1 teaspoon): Introduces an earthy herbal note—dried thyme can also work in a pinch.
Gruyère cheese (1 cup, grated): Melts into a nutty, creamy treasure that binds the tart filling.
Eggs (2 large): Create the custard that holds everything together.
Heavy cream (1 cup): Enriches the filling for a luscious texture.

How to Make french onion tart

Step 1: Caramelize the Onions

Start by heating olive oil and butter over medium heat in a frying pan. Add the thinly sliced onions and sugar to coax out their natural sugars as they gently caramelize. This process takes around 20 minutes and requires patience—stir occasionally to avoid burning. The goal is to achieve a deep golden color and soft texture that builds the tart’s signature sweetness.

Step 2: Season and Cool

Once your onions are beautifully caramelized, sprinkle in the salt, black pepper, and fresh thyme. Stir everything together so those flavors meld. Set the mixture aside to cool slightly—it’s important so the eggs in the filling don’t scramble when combined.

Step 3: Prepare the Pastry Shell

On a lightly floured surface, roll out your pre-made puff pastry to fit your tart pan snugly. Gently press it into the pan and trim any excess. The pastry forms the crisp, buttery vessel that will hold the creamy filling, so make sure it fits well without stretching.

Step 4: Mix the Filling

In a bowl, whisk together eggs and heavy cream until smooth. Stir in the grated Gruyère cheese and then fold in the slightly cooled, caramelized onions. This luscious mixture is the heart of your french onion tart, promising creaminess with a cheesy, savory punch.

Step 5: Assemble and Bake

Pour the filling evenly into the prepared pastry shell, smoothing out the top gently. Pop the tart into your preheated oven at 375°F (190°C) and bake for 30 to 35 minutes. You’ll know it’s ready when the pastry is golden brown and the filling has set to a custardy, sliceable consistency.

Step 6: Cool and Slice

Allow the french onion tart to rest for a few minutes after baking. This helps the filling firm up just enough to slice cleanly while keeping the interior wonderfully creamy. Serve warm or at room temperature for maximum flavor.

How to Serve french onion tart

Garnishes

To elevate your french onion tart experience, consider sprinkling fresh thyme leaves or a light dusting of freshly cracked black pepper over each slice. A handful of chopped chives or a drizzle of extra virgin olive oil adds a nice herbal freshness and shine that brightens every bite.

Side Dishes

This tart pairs beautifully with crisp, green salads tossed in a tangy vinaigrette to cut through its richness. Roasted vegetables or a simple tomato salad with fresh basil can also bring balance and color to your meal.

Creative Ways to Present

Try turning your french onion tart into elegant individual portions by using mini tart pans or tartlets for parties. Layer with caramelized shallots or add a few caramelized mushrooms on top for extra depth. You can even serve thin slices alongside a bowl of French onion soup for a cozy, full-flavored feast.

Make Ahead and Storage

Storing Leftovers

Wrap any leftover french onion tart tightly in plastic wrap or store it in an airtight container in the refrigerator. It should keep well for up to 3 days without losing any of its delightful flavor or texture.

Freezing

If you want to save your tart for later, it freezes beautifully. Wrap it thoroughly in foil and plastic wrap before freezing. When ready to enjoy again, thaw overnight in the fridge and reheat to restore its crispness and creaminess.

Reheating

For the best taste and texture, reheat your tart in a preheated oven at 350°F (175°C) for about 10-15 minutes. This will refresh the puff pastry’s flakiness and warm the filling evenly, much better than a microwave.

FAQs

Can I use other types of cheese instead of Gruyère?

Absolutely! While Gruyère is traditional and offers a wonderful nutty flavor, Swiss cheese or a mild Emmental can be good substitutes. Avoid overly strong cheeses that might overpower the delicate caramelized onions.

Is puff pastry necessary, or can I use pie dough?

Puff pastry is preferred for its flaky, airy texture that contrasts beautifully with the creamy filling. Pie dough will work but results in a denser crust, which changes the overall feel of the tart somewhat.

How long does it take to caramelize the onions?

Caramelizing onions for the french onion tart typically takes about 20 minutes over medium heat. It requires frequent stirring to achieve that deep golden color without burning.

Can I prepare this tart vegan or dairy-free?

You can try by substituting butter with a plant-based alternative, using a dairy-free puff pastry, and replacing Gruyère with a vegan cheese. However, the flavor and texture will be different from the classic version.

What’s the best way to store leftovers?

Store leftovers in an airtight container in the fridge for up to 3 days. To maintain the best texture when reheating, use an oven rather than a microwave to keep the pastry crisp.

Final Thoughts

There’s something truly special about a french onion tart that brings together simple, humble ingredients into a dish bursting with flavor and comfort. I promise, once you make this recipe, it will quickly become a staple you turn to when you want to impress without fuss. So go ahead, grab those onions and puff pastry, and treat yourself to a slice of rich, cheesy, sweet-savory delight that feels like a warm hug on a plate.

french onion tart Recipe

★★★★★

5 from 10 reviews

Author: Sophie
Total Time: 1 hour 15 minutes
Yield: 6 servings 1x
Diet: Vegetarian

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Description

A savory French onion tart featuring caramelized onions, Gruyère cheese, and a flaky puff pastry crust, perfect as a comforting appetizer or light meal.

Instructions

Preheat Oven: Preheat your oven to 375°F (190°C) to ensure it reaches the right temperature for baking the tart evenly.
Caramelize Onions: In a frying pan, heat the olive oil and butter over medium heat. Add the sliced onions and sugar. Cook, stirring occasionally, until the onions are caramelized and golden brown, about 20 minutes. This process develops the deep, sweet flavor of the onions.
Season Onions: Season the caramelized onions with salt, black pepper, and thyme leaves. Stir well to combine and then set aside to cool slightly, allowing the flavors to meld.
Prepare Pastry Base: Roll out the puff pastry on a lightly floured surface to fit your tart pan. Carefully place the pastry into the tart pan, trimming any excess dough to create a neat edge.
Make Cheese Custard: In a mixing bowl, whisk together the eggs and heavy cream until smooth. Stir in the grated Gruyère cheese, then fold in the cooled, seasoned onions. This mixture will form the rich filling of the tart.
Assemble Tart: Pour the onion and cheese custard mixture into the prepared pastry shell, spreading it out evenly to ensure consistent baking.
Bake Tart: Place the tart in the preheated oven and bake for 30-35 minutes, or until the puff pastry is golden brown and the filling is set firmly in place.
Cool and Serve: Allow the tart to cool slightly before slicing. Serve warm or at room temperature to enjoy the full flavors and creamy texture.

Notes

You can substitute Gruyère with Swiss or Emmental cheese if needed.
For a deeper onion flavor, caramelize the onions slowly over low heat for up to 30 minutes.
Puff pastry can be homemade or store-bought for convenience.
This tart is best served the day it is made but can be stored and reheated gently.
Adding a pinch of nutmeg to the custard can enhance the flavor profile.

Prep Time: 20 minutes
Cook Time: 55 minutes
Category: Tart
Method: Baking
Cuisine: French