Onion Tart

March 31, 2008


I first made this tart—Gourmet‘s Onion Tart with Mustard and Fennel—a few weeks ago. And, trust me, I would have loved to post about it right away. But this tart has a super power that stood in the way. That’s right: this is a magically disappearing tart. When I first made it, as a little nibble for guests as they arrived at our bistro-themed Bon Voyage party for my friend Maggie, the tart vanished within mere minutes after I wielded my pizza wheel to slice it into squares.


I could’ve told you about what a joy the tart was to make, with its ethereal, spongy dough that rolled out like a dream and its loooong, slooooow caramelization of slim onion half moons. And I could’ve told you how heavenly the toasted fennel seeds smelled, how fun it was to slather the tart with Dijon mustard or how thrilled I was with the brilliant golden color the tart took on after a brief stint in the oven. But, beyond all this, it would have been a little difficult to describe a tart I didn’t even get to try (!). And, more importantly, how could I entice you with photos of scant crumbs on an empty platter?

(Click “more” for the rest of the story, more photos & the recipe.)


So, when I was home for Easter last weekend and we were pondering potential starters for our Easter Eve dinner, I knew it was just the chance (and the captive audience) I needed for a re-do. And this audience was comprised of family, which means I can boss them around. They might roll their eyes when I swat away the hands reaching in for a square before my photo shoot was complete, but they have to love me.


Now that I’ve got photos, I can show you how elegant this tart is. But, even better, I can describe it to you, because this time, there was a square to spare! Let’s start with the crust, which was cracker-thin and slightly salty; in short, a backdrop begging for a delicious adornment. Which brings me to the slick of Dijon coating the crust, which added a complex and unexpected dimension to the tart. And then we arrive at the onions. If you’ll excuse me for just one moment, I need to quickly swoon.


Okay, I’m back. Sorry about that—but this melty onion topping is entirely swoon-worthy. Apparently, when you allow thinly-sliced onions to bask over low heat in a fennel seed-spiked pool of olive oil for longer than an hour, onions that were once crunchy and abrasive will do quite an about-face. They will become supple and mild and just-this-side-of-sweet and (if I hadn’t made myself clear already) totally irresistible. In fact, I was shocked that such a truncated list of ingredients could yield an end product so transcendent. So, please, make this tart. And, when you do, take care to ensure that your fellow diners are not the types who will mind when you throw a sharp elbow as you dive in. Because when the dust settles, all that will remain will be crumbs. Or, if you’re very lucky, a stray onion.

Onion Tart with Mustard and Fennel

2 1/4 teaspoons active dry yeast (a 1/4-ounce package)
1/2 cup warm water (105-115°F)
1 1/2 to 1 3/4 cups all-purpose flour
1 large egg
1/3 cup plus 1 tablespoon extra-virgin olive oil, divided
2 1/2 teaspoons salt, divided
2 teaspoons fennel seeds
3 pound yellow onions, halved and thinly sliced
1 tablespoon Dijon mustard
1/2 cup grated Parmigiano-Reggiano

Stir together yeast and warm water in a small bowl and let stand until foamy, about 5 minutes. (If mixture doesn’t foam, start over with new yeast.)

Put 1 1/2 cups flour in a medium bowl, then make a well in center of flour and add yeast mixture to well. Stir together egg, 1 tablespoon oil, and 1 1/2 teaspoons salt with a fork. Add egg mixture to yeast mixture and mix with a wooden spoon or your fingertips, gradually incorporating flour, until a soft dough forms. Transfer dough to a floured surface and knead, working in additional flour (up to 1/4 cup) as necessary, until smooth and elastic, about 5 minutes. Transfer dough to an oiled bowl and turn to coat. Cover with plastic wrap and let rise in a draft-free place at warm room temperature until doubled, 1 to 1 1/2 hours.

While dough rises, heat remaining 1/3 cup oil in a 12-inch heavy skillet over medium-high heat until it shimmers, then sauté fennel seeds until a shade darker, about 30 seconds. Stir in onions, remaining teaspoon salt, and 1/2 teaspoon pepper, then reduce heat to medium-low and cover onions directly with a round of parchment paper. Cook, stirring occasionally, until onions are very tender and golden brown, 1 to 1 1/4 hours.

Preheat oven to 375°F with rack in middle.

Knead dough gently on a floured surface with floured hands to deflate. Pat out dough on a large heavy baking sheet (preferably blue steel) into a 15- by 12-inch rectangle, turning up or crimping edge, then brush mustard evenly over dough, leaving a 1/2-inch border around edge. Spread onions evenly over mustard, then sprinkle evenly with cheese.

Bake tart until crust is golden brown, 30 to 35 minutes. Cut into 2-inch squares or diamonds and serve warm or at room temperature.


19 Responses to “Onion Tart”

  1. Megan Renee Says:

    I am a mustard fanatic and I will be making this on Thursday for our dinner party. It looks so delicious, thanks for posting!

  2. This is one baked good my husband will definitely eat. It looks wonderful – tks for sharing!

  3. This looks fantastic, I can almost taste the savour flavour, you have me wanting one right now!!!

  4. Maggie Says:

    I can vouch for the deliciousness for this one – I was one of those who elbowed others for last few bites (after having eaten perhaps 1/4th myself). And I love the pictures!

  5. michelle Says:

    my love of caramelized onions knows no bounds, and is my favorite way to eat them! i’m going to have to give this crust a whirl, it sounds yummy. and great pix!

  6. RecipeGirl Says:

    You sure have been picking some winners lately! Looks really, really good 🙂

    I had to laugh at your comment about taking pics and having family wait to eat your creation. Been there, done that… funny stuff!

  7. Emily Says:

    I feel personally responsible for the fact that you didn’t get to try the tart on the first go-round. I would apologize, but I think you made your own bed when you created that tart. It was amazing!

  8. Astrid Says:

    Oh my. I usually bake sweets, but this I’ve *got* to try. Thank you!

  9. Kristin at The Kitchen Sink Says:

    Megan Renee: I’m a big fan of mustard too. Usually, the spicier and grainier the better. I think you’ll like how subtly assertive the Dijon is in this tart. Let me know how it goes! Have fun at your dinner party.

    Patricia, Rachel: Thanks!

    Maggie: You are very diligent about vouching for the foods you’ve eaten! The mental picture of your five-foot self elbowing several of the six-footers in attendance out of the way is making me laugh. (With you! With you! Not at you …)

    Michelle: I thought that there was nothing that could possibly make caramelized onions taste any better, but the toasted fennel seeds are a brilliant addition.

    RecipeGirl: That’s what family’s for, right?

    Emily: Well, I’m glad that you and Maggie have owned up to the tart’s disappearance. And here I thought it was magic. Anyway, thanks for commenting! We need to get together soon — I haven’t seen you in forever (since the night of this tart, maybe?).

    Astrid: Well you do get to bake (the crust) and the onions are very nearly sweet, so it’s almost like baking sweets, right? Give it a go! Let me know what you think.

  10. eggsonsunday Says:

    I just made this, and it is delicious!! Love the fennel and dijon with the sweet onions. –Amy

  11. This just sounds delicious! I have a new found love for caramelized onions and love them on a tart/pizza. I will have to give this a try!

  12. Kristin at The Kitchen Sink Says:

    Amy: So glad you enjoyed it!

    Gretchen: This is a spectacular showcase for the onions. Hope you give it a try …

  13. […] this flatbread became our watch-the-thunderstorm appetizer. I used the crust from the caramelized onion tart Kristin posted about (which is also really delicious!), substituting half white whole wheat flour. […]

  14. Polly Says:

    I happened upon your *divine* website recently and have been chomping at the bit to have an excuse to try this recipe (among many, many others here). What could be more perfect than six close friends willing to gather for good wine and another one of my “appetizer experiments”? Smashing success. p.s. I love how you marry your everyday life with each recipe!

  15. Polly: Thanks for your kind words! I’m so glad you tried this recipe. It’s such a keeper. I need to look for a reason to make it again soon.

  16. deb smith Says:

    I know I’m coming in on the conversation very late in the game here, but just wanted to comment/ask. First, caramelized onions are like crack to me. Had them on gorgeous steaks last night. I was wondering if I could use fresh or frozen pizza dough in place of making the dough myself. I am not a baker and messing with yeast and flour is new territory I’m not willing to explore today. I’d like to make this for company tonight.

    Thank you

  17. Hi Deb: Yes, I think you could use store-bought pizza dough. This is a pretty easy dough, but I’m guessing that you’ve got a little too much going on today for daring baking adventures! But, maybe next time? Let us know how it turns out! Happy New Year.

  18. Cheryl Says:

    made it with frozen puffed pastry. Great recipe

  19. Cheryl: That’s great to hear! Thanks for reporting back!

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