A rustic and savory French tart made with sweet, slow-caramelized onions and a creamy egg custard nestled in a flaky, buttery crust. This elegant yet simple dish is golden, cheesy, and deeply flavorful with every slice—a perfect centerpiece for brunch, lunch, or a light dinner.

Why You’ll Love This Recipe

This Classic French Onion Tart is a celebration of rich, comforting flavors in a refined presentation. The long, slow caramelization of onions brings out their natural sweetness, perfectly balanced by the creamy custard and nutty Gruyère cheese. It’s an excellent make-ahead dish that tastes just as good at room temperature as it does warm from the oven. Whether you’re entertaining guests or preparing a cozy weekend meal, this tart is sure to impress.

Ingredients

(Tip: You can find the complete list of ingredients and their measurements in the recipe card below.)

For the crust:

• 1 1/4 cups all-purpose flour
• 1/2 cup cold unsalted butter, cubed
• 1/4 teaspoon salt
• 3–4 tablespoons cold water

For the filling:

• 3 large yellow onions, thinly sliced
• 2 tablespoons olive oil
• 1 tablespoon unsalted butter
• 1/2 teaspoon salt
• 1/4 teaspoon black pepper
• 1/4 teaspoon dried thyme
• 3 large eggs
• 1/2 cup heavy cream
• 1/2 cup milk
• 1/2 cup grated Gruyère cheese

Directions

1. Make the crust: In a mixing bowl, combine the flour and salt. Add cold, cubed butter and cut it in using a pastry cutter or your fingers until the mixture resembles coarse crumbs. Gradually add cold water, one tablespoon at a time, mixing until the dough comes together. Wrap in plastic wrap and chill for 30 minutes.
2. Preheat the oven to 375°F (190°C). Roll out the chilled dough on a floured surface and transfer it to a 9-inch tart pan. Trim the edges and prick the base with a fork to prevent puffing.
3. Blind bake the crust: Line the crust with parchment paper and fill with pie weights or dried beans. Bake for 10 minutes, remove weights and paper, and bake for an additional 5 minutes. Set aside to cool.
4. Prepare the filling: In a large skillet, heat olive oil and butter over medium heat. Add the sliced onions and cook slowly, stirring regularly, for 25–30 minutes until deeply golden and caramelized.
5. Season the onions with salt, pepper, and thyme, then allow to cool slightly.
6. In a separate bowl, whisk together eggs, cream, and milk. Stir in the caramelized onions and grated Gruyère.
7. Assemble the tart: Pour the filling into the pre-baked crust and spread evenly. Bake for 30–35 minutes or until the custard is set and the top is golden brown.
8. Let cool for at least 10 minutes before slicing. Serve warm or at room temperature.

Servings and timing

Servings: 6–8 slices
Prep Time: 20 minutes
Cook Time: 65 minutes (includes caramelizing onions and baking)
Chill Time: 30 minutes (for the dough)
Total Time: 1 hour 55 minutes

Variations

• Cheese Swap: Use Emmental, Comté, or sharp white cheddar instead of Gruyère.
• Add Protein: Include cooked bacon or pancetta for a richer, meatier tart.
• Herb Upgrade: Add fresh thyme, chives, or parsley to the custard for a more aromatic flavor.
• Shortcrust Alternative: Use store-bought pie crust for convenience.
• Mini Tarts: Make individual tartlets using a muffin tin for bite-sized portions.

storage/reheating

Store leftovers in an airtight container in the refrigerator for up to 3 days. Reheat slices in a preheated oven at 350°F (175°C) for about 10–15 minutes or until warmed through. The tart can also be enjoyed cold or at room temperature.

FAQs

Can I use store-bought crust?

Yes, a high-quality store-bought shortcrust or pie crust works well and saves time.

Can I make this tart ahead of time?

Absolutely. Prepare the tart a day ahead and reheat before serving, or serve it at room temperature.

What onions are best for this tart?

Yellow onions are ideal for caramelizing due to their balanced sweetness and flavor.

How do I know when the onions are properly caramelized?

They should be soft, golden-brown, and sweet, which typically takes about 25–30 minutes on low heat.

Can I freeze this tart?

Yes. Freeze the fully baked and cooled tart wrapped tightly in plastic and foil for up to 1 month. Thaw in the fridge before reheating.

Is milk necessary, or can I use all cream?

You can use all cream for a richer custard, though the combination of milk and cream offers a balanced texture.

Can I use a quiche pan instead of a tart pan?

Yes, as long as it has a removable bottom, it will work just fine.

What can I serve with this tart?

Serve with a light green salad, roasted vegetables, or a bowl of soup for a complete meal.

Can I use red onions instead?

Red onions can be used, but they will result in a slightly different flavor and a darker color.

Is it possible to make this tart without eggs?

Eggs are essential for the custard structure. For an egg-free version, consider making a caramelized onion galette instead.

Conclusion

This Classic French Onion Tart is a timeless recipe that captures the rich, buttery essence of French cuisine. With its deeply caramelized onions, creamy custard filling, and flaky crust, it’s a dish that’s both comforting and refined. Whether you’re planning a brunch, a picnic, or an elegant dinner, this tart is a versatile and impressive option that will delight any table.

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