This Savory Tarte Tatin Is French Onion Soup in a Tart

Combine the classic bistro soup with a Tatin for the fanciest caramelized onion tart around.

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The arrival of colder weather means it's time to get back to comforting hearty food, and the French have that category covered. I've started planning my meals for an upcoming trip to Paris over the holidays, and my mind started wandering to classic bistro dishes like steak au poivre.

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These daydreaming moments often end up as recipe brainstorming sessions for me, and I soon had an idea stuck in my mind: what if I mashed up French onion soup and classic tarte Tatin into a savory onion tart with the flavors of the classic soup?

Full disclosure: I don't love French onion soup or apple tarte Tatin. I usually find the soup to be way too heavy, and I'm over it after a few bites. And I'm not a big fan of soft, cooked apples, especially when they get sweetened even more with caramel. But this tart idea I could get behind.

I love the interplay of bitter and sweet in caramelized onions, and who doesn't love a buttery tart crust? Throw in some gooey Gruyère and meaty stock and I am all in. So I got to work to figure out the best way to make this delicious Francostein monster.

The Crust: Pie or Puff?

Rolling out pie dough

For the crust of a tarte Tatin, you can decide whether to make dough from scratch, or take the quick and easy route by using frozen puff pastry. I'm not a professional baker, nor am I here to throw shade at the store-bought crowd, but I will happily push the BraveTart agenda: Stella's old-fashioned flaky pie dough makes the best French onion tarte Tatin.

A slice of tarte tatin sprinkled with chives on a small plate, with a ramekin of chives and the rest of the tart on the side.

I tested with both throughout the recipe development process, and tasters unanimously preferred tarts made with pie dough over puff pastry. The pie dough tarts were more cohesive; the crust has structure and a pleasant chew, and it melds seamlessly with the caramelized onions and melty Gruyère cheese.

A finished puff pastry tarte Tatin

The puff pastry versions are a little more disjointed: The onions don't set in the pastry as well during the baking process, and the less-porous puff pastry traps more steam from the onions, which hinders browning and makes them softer in the process. That said, the tart is still real tasty even when made with puff pastry. And the process for preparing the crust is pretty much the same for both pie dough and puff pastry.

Photo collage of rolling out pie dough and trimming it into a round by using an inverted skillet as a guide.

I start by rolling out the dough (half a batch of Stella's pie dough or one sheet of thawed puff pastry) on a well-floured board until it's large enough to cut out a 10-inch round. An inverted skillet (the same one you will use for the tart itself) is a good guide for trimming the dough circle.

Photo collage of a round of pie dough being transferred to a piece of parchment set on an inverted rimmed baking sheet.

Brush off excess flour from the dough and, with the help of your rolling pin, transfer the round to an inverted baking sheet lined with parchment paper.

Crimping the pie dough round to make a raised edge, and a 9-inch dough circle.

Working around the edge of the dough, fold over a 1/2-inch border of dough, pinching it together to form a raised rim, which will help keep the onions contained and in place for the tart. Once you have completed this step, your crust should be 9 inches in diameter.

Docking puff pastry round with a fork

It's important to "dock" the dough (baking-speak for poking holes in it) to allow some steam to escape during baking; cut three slits in the crust if using pie dough, and for puff pastry you can poke the round all over with a fork. Pop the sheet tray in the fridge to chill the dough while you work on the onion filling.

The Onions: Sweet, Small, or Savory?

Closeup side view of finished tarte tatin on a serving platter.

For his French onion soup recipe, Daniel recommends going with a mix of allium varieties for a soup with the most complex flavor. I briefly entertained the idea of trying to mix and match alliums for this tart, but realized early on that it would just further complicate an already involved recipe. I needed to simplify as much as possible and go with one type of onion, so I began testing with Daniel's recommended all-purpose variety: yellow onions.

Photo collage of three early test batches of onion tarte tatin. The first is made with yellow onions, chicken stock, and has Dijon mustard spread on the underside of the crust. The second is made with yellow onions and beef stock. The third is made with vidalia onions and chicken stock.

Unlike Goldilocks, I quickly realized that my first choice was just right. Yellow onions have a middle-of-the-road allium flavor, neither too sweet nor too harsh, and a relatively low moisture content that makes them great for caramelizing, and their manageable size ended up being ideal for tart-building.

After spending way too long peeling dozens of cute cipolline and shallots for initial test tarts, I knew it would be cruel to subject people to that tear-inducing monotony. I wanted something more appealing and less a-peeling. With tiny alliums out of contention, I ran a side-by-side test comparing tarts made with yellow onions and Vidalias, and as suspected, the Vidalia tarte Tatin veered into too-sweet territory.

The Filling: Caramel or Caramelized?

Photo collage of cutting onions into wedges for the tarte tatin. After halving and peeled the onions, carefully cut away the scraggly part of the root end, leaving the white part of the root end still attached. The onions are then cut into wedges that are kept intact through the root end.

Once I had the winning onion, I had to figure out the amount to use, and three small-ish yellow onions ended up fitting the bill (look for onions that weight about half a pound each, and are about 3 inches in diameter). I knew that I needed larger onion pieces with a flat surface to stand in for the fruit in a classic Tatin, so I started by cutting two onions into wedges through the root end, keeping the root attached but trimming off the scraggly part at the very end. Two onions will give you 16 wedges, the perfect amount for fitting into a 10-inch skillet.

Two onions cut into wedges and one sliced thin for the tarte tatin.

In a classic Tatin, the fruit releases pectin-rich juices as it cooks on the stovetop, creating a glossy, sticky caramel with the butter and sugar in the skillet, which then binds the fruit together in the tart. Onions aren't as rich in pectin as apples, and don't cook down as readily, so I needed to find a way to recreate that binding effect without making the tart overly sweet in the process.

Tarte Tatins from the first round of testing.

For my first round of testing, I tried two different methods to achieve this result. One was to make a wet caramel, using onion juice (purée raw onions with a little water, or use a juicer) instead of water, that I then loosened with chicken stock. This was a little trick I had picked up from one of the restaurants I worked at, where we made an onion caramel-chicken jus.

When the onion caramel is combined with an intense restaurant-style jus, everything works together—the sweetness of the caramel balanced by the savory intensity of the ultra-reduced, wine-fortified stock. This quick at-home version ended up being too sweet, because store-bought chicken stock doesn't have enough savory intensity to stand up to the caramel. This tart wasn't meant to be dessert, so I ditched the onion caramel.

Caramelized onions cooked to a jammy consistency.

My second approach was to make a jammy caramelized onion filling to nestle into the negative space between the onion wedges in the tart. I needed to also find a way to incorporate the other flavors of French onion soup—meaty stock, sherry, thyme—into the tart, and this caramelized onion mixture proved to be the vehicle for those flavors, too.

Adding thinly sliced onions to a saucepan with melted butter.

Start by thinly slicing the third onion, and sweating it in a saucepan with a little butter. Normally, I like to take the time to slowly cook a proper batch of caramelized onions, but when you're only cooking one onion, you can speed up the process.

Photo collage showing progression of sliced onions caramelizing in a saucepan.

Lightly season the onion with salt to help coax out its liquid, and cook it over medium-high heat, stirring frequently. The onions will begin to stick and form a brown fond on the bottom of the pan, which you'll loosen by adding a tablespoon or two of water at a time and scraping up the brown bits from the bottom and sides of the pot.

Adding sherry and chicken stock to caramelized onions.

Keep repeating this process until the onions are soft, sweet, and a deep golden brown, and then deglaze them one last time with dry sherry instead of water. Next, add in some stock (chicken or beef, more on that in a minute), and cook it down until the onions are jammy, and the liquid has reduced to just coat the onions.

Photo collage of finishing steps for caramelized onion mixture. Adding cider vinegar, fish sauce, chopped thyme, and then cooking onions down until almost all of the liquid has evaporated.

Finish them with a splash of cider vinegar and fish sauce (an optional background savory boost), and some chopped thyme leaves. Once there is very little liquid left in the saucepan, set the onions aside to cool while you build the tart.

The Stock: Chicken or Beef?

Overhead of finished tarte tatin on a yellow serving plate with a ramekin of chives next to it and a small blue plate.

A quick aside on what kind of stock you should use for this tart. The short answer: whichever meaty stock you have available. I tested with our homemade beef stock as well as with two varieties of store-bought chicken and beef stocks.

They all worked, and tasters were not able to distinguish between them, which makes sense seeing as there is very little stock that goes into the onions (compared with the amount that goes into a batch of French onion soup). For store-bought stock, just make sure you go with a low-sodium option, or else you will have to be much more careful with seasoning so that the tart doesn't end up too salty.

The Skillet: Stainless Steel or Cast Iron?

Photo collage comparing a tarte tatin made in a stainless steel skillet vs. one made in a cast iron skillet.

For building the tart, you will need a 10-inch skillet that needs to be oven-safe. You can decide whether to use cast iron or stainless steel, depending on your eyesight and arm-strength. You need to be able to keep an eye on how dark the sugar gets as it caramelizes in the skillet, and this is much easier to track on the shiny grey of stainless steel than on the black matte finish of cast iron.

Onions cooking and sugar caramelizing in a cast iron skillet and a stainless steel skillet.

After baking, you also need to be able to invert the skillet over a plate. Cast iron is a lot heavier than stainless steel, so it's worth testing your comfort with some skillet bicep curls before you start building your tart.

Photo collage of four finished tarte tatins. Top left: stainless steel skillet, pie crust. Top right: cast iron skillet, pie crust (this one has the deepest and most even caramelization). Bottom left: stainless steel skillet, pie crust, and used toasted sugar. Bottom right: stainless steel skillet, puff pastry crust.

Despite being heavier and harder to see into, cast iron does achieve deeper and more even caramelization on the onions in the tart. If you can bear the weight, I'd recommend going with cast iron. Stainless steel won't let you down though, and can still give you excellent tart results. Unfortunately, due to their flared shape, 10-inch carbon steel skillet don't have as much surface area as most stainless or cast iron skillets, so they can't be swapped in without altering the recipe.

Photo collage showing preparing skillet for the onion wedges by smearing it with butter and sprinkling with sugar and salt.

Once you have your skillet of choice, smear it with a few tablespoons of softened butter and then evenly sprinkle one tablespoon of sugar over the butter.

Photo collage of onion wedges being placed into a skillet that has been buttered and sprinkled with sugar and salt.

After a light seasoning of salt and pepper, I arrange the onion wedges in a tight formation in the skillet, making sure they are in even contact with the pan. Arranging them in an unheated pan is way easier than trying to nestle in the onions after melting the butter and sugar together in a skillet. As you may have noticed in one of the photo collages above, I tested tarts using Stella's toasted sugar to see if it would lead to deeper flavor and more even caramelization. With only one tablespoon of sugar in the recipe, the effects weren't noticeable. If you have a batch of toasted sugar kicking around in your pantry, you can certainly use it, but it won't make or break the tart.

Cooking onion wedges over high heat in a skillet.

Cook the onion wedges on high heat, without stirring the skillet, until the sugar turns a deep amber color. Stove burners don't heat evenly, so you will need to move the skillet around to promote even browning.

Spooning caramelized onion mixture in between onion wedges in the skillet.

Spoon the caramelized onion mixture in the spaces between the onion wedges, and continue cooking just long enough to meld everything together.

Photo collage of sprinkling cheese over the onions in the skillet, and topping with the round of pie dough before transferring the skillet to the oven.

Top the onions with a handful of shredded Gruyère, and then pop the dough lid over the whole deal. You don't want the crust to be sticking to the sides of the skillet, as that will make it hard to unmold after baking.

Photo collage of spreading Dijon mustard on pie crust before placing it in the skillet with the onions.

If you want some subtle acidity and bite in your tart, you can spread some Dijon mustard on the underside of the crust before you place it in the skillet. I tested the tarts with and without mustard, and liked how the subtle heat of the mustard offsets some of the sweetness from the onions.

The Bake and the Flip: Golden or Dark, Cool or Warm?

A pie dough tarte Tatin baked in a stainless steel skillet

I found that it's important to bake the crust to a deep golden brown for this tart. If you pull it out of the oven while the crust is still blond, it will turn soggy once the tart has been inverted and has to support the weight of the onions. So let the crust take on plenty of color before you take the tart out of the oven.

Photo collage of process of inverting and unmolding tarte tatin onto a serving plate.

Unfortunately, the most stressful part of the recipe comes at the very end, when it's time to invert the skillet to release the tart onto a plate. While it may be tempting to let the tart cool completely in the skillet before attempting the flip, don't. If you let the tart cool for too long, the sugar will harden, and unmolding will become a lot trickier.

Let the skillet cool for just a few minutes, and then get your flip on. The key here is confidence. Know that it will release, and you will be a tart champion. Get a large plate, secure it over the skillet, and then invert it confidently. Let gravity do its thing, rather than trying to shake it loose if it doesn't release instantly. You'll feel it when the plate gets heavier, and you uncover your masterpiece.

Overhead of finished tarte tatin on a yellow serving plate with a ramekin of chives next to it and a small blue plate.

As with your bags in an overhead luggage bin, some onions may have shifted during flight, so now is the time to rearrange any that have fallen out of place. Slide the tart onto a wire rack to finish cooling (otherwise you risk steaming the bottom crust). Once the tart has cooled down, you're good to slice, but make sure you show off your tart skills to guests before serving. Then blow everyone away with your French soup in a tart costume.

Side view of a slice of tarte tatin on a small plate with the rest of the tarte tatin in the background.