The Ultimate French Onion Tart Recipe

My au pair job entails that I cook for the French family I live with. It’s not something I talk about often on this blog, but cooking is a huge part of my life here and is one of my daily joys (and stresses, ha). So I wanted to share my French onion tart recipe (French: tarte à l’oignon). It’s a simple tart that tastes just like French onion soup… yum!

French Onion Tart Recipe
My favorite brand of pre-made crust in France.

French Onion Tart Recipe

Hint- though I didn’t use them, this recipe is even more delicious with lardons, a.k.a. bacon.


  • One 9- or 10-inch (23-25 cm) tart pan
  • Whisk
  • Wooden spoon
  • Small pot
  • Chef’s knife
  • Cutting board
  • Medium-sized saucepan

Béchamel sauce ingredients:

  • 1 tablespoon butter
  • 1 tablespoon flour
  • 1/2 cup of milk (120 mL)
  • salt and freshly ground black pepper

Tart ingredients:

  • 4 small yellow onions (around 400g)
  • 1 pie crust (pâte brisée or short-crust pastry)
  • Grated gruyère (about a 1/2 cup)
  • Salt and pepper

Part 1: Make the béchamel sauce

Béchamel sauce is a white, flour-based sauce that is used in tons of French dishes- it’s always the same procedure so here are the basic steps.

  1. Put butter and flour in a small pot over medium heat.
  2. Stir with a wooden spoon until they’re combined.
  3. Pour in the milk. Whisk there are no lumps.
  4. Season with salt and pepper.
  5. Set aside.
The béchamel sauce should look like this when finished.

Part 2: Caramelize the onions

  1. Preheat the oven to 390ºF (200ºC).
  2. Peel and chop the onions. And your knife cuts don’t have to be perfect! Lord knows mine aren’t.
  3. Then start sauteeing the chopped onions in a sauce-pan over medium heat with a generous knob of butter (a noisette in French, about 2-3 tablespoons). Sautee until they caramelize, about 30 minutes.
  4. Set the pan aside.
This is the step where I’m always tempted to just put them in the tart… but they’re not done yet.
Now they’re done.

Part 3: Assemble the tart

1. Gently place the pie crust in the tart pan. You can either use your own wax paper or the wax paper that comes with the pie crust.

2. Take a fork and poke holes in the bottom of the crust.


3. Pour the béchamel sauce into the pan with the caramelized onions. (You may not need all of it, just put enough to cover the onions.)


4. Carefully pour the mixture into the pie crust.


5. Sprinkle grated gruyère on top.

6. Place the tart into the preheated oven. And bake it until it looks like this!


Just kidding. This is the one that Julia accidentally burned when pre-heating the oven to make cookies. This one’s better.


Voila, it’s done! Now eat, enjoy and impress all of the French people you know! It’s best served with a simple butter lettuce salad with a light vinaigrette.

*This recipe is adapted from the classic recipe of the wonderful French home-cook, Françoise Bernard.

So, your turn. Which French dishes do you love to cook?

P.S. Tarte Flambée Recipe: Alsatian Pizza with Bacon, Crème Fraîche and Onions and Authentic Quiche Lorraine Recipe (With Bacon and Gruyère).

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About Ashley Fleckenstein

Ashley is a travel and lifestyle blogger who lives in Ann Arbor, Michigan. Since college she has au paired in Paris, backpacked the world solo, and lived in Uganda. Her work has been featured by Buzzfeed, Forbes, TripAdvisor, and Glamour Magazine.

15 thoughts on “The Ultimate French Onion Tart Recipe”

  1. this is a bit like a quiche, a bit like a Flammkuchen from Alsace. What I recently cooked is more on the sweet side and is called “tarte Tatin”!

  2. From the looks of your photo you are becoming an excellent chef. It looks so good, but lots of calories, correct? Oh well, almost all good food is fattening. Just have have to eat smaller portions
    Love, Gamma

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