Name: French Onion Tart Recipe
Prep time: 20 min
Cook time: 1 h
Total time: 1 h 20 min
Cuisine: French
Ingredients: 1 9-inch pie crust; 2 tbsp butter; 3 medium yellow onions, thinly sliced; 1 tsp thyme; Salt & pepper to taste; ¾ cup heavy cream; 2 eggs; ½ cup grated gruyère or Swiss cheese; Pinch of nutmeg

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Picture this: a buttery, flaky tart shell, golden at the edges and spilling over with sweetly caramelized onions, all nestled in a creamy custard scented with fresh herbs and cheese. The French Onion Tart is a showstopper that’s equally at home on a festive brunch table or as the star of a cozy lunch. Imagine all the beloved flavors of classic French onion soup—now transformed into an elegant, easy-to-slice tart you won’t be able to resist sharing with friends and family.

Ingredients You’ll Need

French Onion Tart is all about a few humble ingredients coming together to create something truly special. These kitchen staples each play a key part in making the tart so irresistible, layering sweet, creamy, cheesy, and savory notes into every bite.

1 9-inch pie crust: The foundation for your French Onion Tart; use homemade for extra flavor or a good quality store-bought crust to save time.
2 tbsp butter: Essential for getting those onions meltingly tender and deeply golden—don’t skimp here!
3 medium yellow onions, thinly sliced: The stars of the show, these onions will caramelize into a sweet, jammy layer.
1 tsp thyme: Adds fragrant, earthy depth and that unmistakable French touch.
Salt & pepper to taste: Seasonings that bring all the flavors into balance—taste as you go.
¾ cup heavy cream: Rich and silky, this creates the custardy base that holds the tart together.
2 eggs: Eggs thicken the filling and ensure a gorgeous sliceable set.
½ cup grated gruyère or Swiss cheese: For savory, nutty flavor and a beautifully melty texture.
Pinch of nutmeg: Just a whisper adds warmth and complexity, lifting all the other flavors.

How to Make French Onion Tart

Step 1: Prep the Tart Shell

Start by preheating your oven to 375°F (190°C). Lay your pie crust into a 9-inch tart pan, gently pressing it into the edges and trimming any overhang. Prick the base all over with a fork—this helps prevent bubbles—then give it a quick pre-bake for 10 minutes. This step keeps the bottom crisp, so it can stand up to the lush filling of your French Onion Tart.

Step 2: Caramelize the Onions

While the crust is in the oven, set a large skillet over medium-low heat and melt the butter. Toss in your sliced onions, thyme, a good pinch of salt, and plenty of freshly ground black pepper. Let them cook slowly, stirring occasionally for 20 to 25 minutes. You’re looking for a deep golden color and a sweet, jammy aroma—the signature base for your French Onion Tart. Low and slow really is the secret here!

Step 3: Make the Creamy Custard

In a mixing bowl, whisk together the heavy cream, eggs, grated cheese, a pinch of nutmeg, and another little hit of salt and pepper. This is where the French Onion Tart gets its supremely luscious, custardy filling. The cheese will melt into the custard, tying everything together when baked.

Step 4: Assemble the Tart

Once your crust and onions are ready, spread the caramelized onions in an even layer over the prebaked shell. Next, carefully pour the creamy custard mixture over the onions, making sure it seeps down into all the oniony nooks and crannies. The mixture should just cover the onions, promising a creamy bite in every forkful.

Step 5: Bake to Golden Perfection

Slide the assembled French Onion Tart into your oven and bake for about 30 to 35 minutes, or until the custard is set and lightly golden on top. If you see the edges browning too quickly, loosely tent the tart with foil. Let it cool for a few minutes before slicing—this makes cutting easier and stops the filling from running.

How to Serve French Onion Tart

Garnishes

Nothing beats the finishing touch of a shower of freshly chopped herbs (like parsley or more thyme) over your French Onion Tart just before serving. For a flash of color and a little zing, you can even add a tiny sprinkle of flaked sea salt or freshly cracked black pepper. A light brush of melted butter on the tart edge never hurt, either!

Side Dishes

This tart loves the company of a crisp green salad tossed with vinaigrette—the acidity cuts through the richness beautifully. A bowl of marinated olives, a few slices of prosciutto, or a handful of cherry tomatoes on the side all make lovely, simple additions. If you’re serving it for brunch, a bowl of fresh fruit or a cool cucumber salad balances out the flavors perfectly.

Creative Ways to Present

Try serving your French Onion Tart as small squares or wedges for an elegant appetizer tray—it’s delightful both warm and at room temperature. You can also make mini tarts in muffin tins for hand-held treats, perfect for picnics or parties. A drizzle of balsamic glaze or a dollop of crème fraîche on each slice adds a truly sophisticated flair.

Make Ahead and Storage

Storing Leftovers

If you’re lucky enough to have any French Onion Tart leftover, pop slices into an airtight container and refrigerate for up to three days. The flavors keep developing and mingling, sometimes tasting even better the next day.

Freezing

The French Onion Tart freezes beautifully! Simply wrap the cooled tart (either whole or sliced) tightly in plastic wrap and then foil. Freeze for up to two months. Let thaw overnight in the fridge before reheating for best texture.

Reheating

Warm up slices of French Onion Tart in a 325°F (165°C) oven for about 10 to 15 minutes, or until heated through. Skip the microwave if you can—it tends to soften the crust. For a just-baked crisp edge, a quick toast in the oven works wonders.

FAQs

Can I use a different kind of cheese?

Absolutely! While gruyère or Swiss give that classic nutty flavor, sharp white cheddar or even fontina work well in this French Onion Tart if you want a twist. Go with what sounds tastiest to you.

Do I have to use a tart pan?

Not at all. You can use a standard 9-inch pie pan if that’s what you have handy. Your French Onion Tart may look a bit more rustic, but it’ll taste every bit as wonderful.

Can I make the tart shell from scratch?

Definitely, and it’s a great way to add personality! A homemade buttery crust really elevates a French Onion Tart. But no shame in using a good premade one for busy days—no one will complain!

Is it okay to caramelize the onions in advance?

Yes, prepping the onions ahead is a major time-saver. Store them in an airtight container in the refrigerator for up to two days until you’re ready to assemble your French Onion Tart.

Can I make this tart vegetarian?

You bet! The base recipe is vegetarian as is. For extra depth, you could add a sprinkle of vegetarian-friendly parmesan or a smattering of fresh herbs for extra punch.

Final Thoughts

If you haven’t tried making a French Onion Tart before, this is the perfect recipe to start with—it’s unfussy, packed with flavor, and guaranteed to earn rave reviews around your table. Give it a whirl, and let yourself fall in love with this simple French classic!