Rustic Onion Tart

Is there nothing better than caramelized onions? Yes, they take some time to make, but they’re not hard to cook, and it’s so so worth the effort.

Here is great way to enjoy them—in a simple rustic tart, with some shredded Gruyere cheese and a sprinkling of thyme. You can either use a ready made frozen crust (the flat or folded kind), or make your own crust.


Rustic Onion Tart Recipe

  • Prep: 20 minutes
  • Cook: 1 hour, 40 minutes
  • Yield: Serves 4


  • 1 recipe for butter sour cream pastry dough* or 1 packaged, flat pie crust (Trader Joe's has one in their frozen section)
  • 3 medium sized red and/or yellow onions (enough for 5 to 8 cups, sliced)
  • 2 Tbsp olive oil
  • 1 Tbsp butter
  • Salt
  • 1 teaspoon balsamic vinegar
  • 1/2 teaspoon fresh thyme, chopped, or 1/4 teaspoon dried thyme
  • 3/4 cup (not packed) roughly grated Gruyère Swiss cheese

*Sour cream pastry dough:

  • 1 1/4 cup (160 g) all purpose flour
  • 1 teaspoon salt
  • 5 ounces of butter (1 1/4 sticks, 10 Tbsp, 137g), cubed
  • 1/4 cup sour cream


1 If you are making a crust from scratch, prepare the dough and let it chill in the refrigerator while you are cooking the onions. To prepare the dough, whisk the flour and salt together in a large bowl. Cut the butter into the flour with your hands or with a pastry cutter, until the mixture resembles a coarse meal. Add the sour cream and use a fork to incorporate it into the dough. Gather the dough into a ball and shape it into a disk. Wrap it with plastic wrap and chill for at least an hour.

2 Peel and slice the onions, lengthwise from stem to root. (See How to Slice an Onion)

3 Heat olive oil and butter in a large, heavy-bottomed sauté pan on medium heat. Once the butter has melted, add the onions and sprinkle a little salt over them. Cook, stirring occasionally for 10 minutes, until the onions have softened and are translucent.

Reduce the heat to medium low and cook for an additional 40 minutes, stirring occasionally, until the onions are well browned. Add balsamic vinegar and cook for 10 minutes more, until onions are completely caramelized. Remove from heat.

4 Preheat the oven to 450°F. Remove the dough from the refrigerator and let stand for 5 minutes before rolling it out. Roll out the dough on a lightly floured surface to a 13-inch diameter. Remove the crust dough to a cookie sheet lined with parchment paper.

5 Place all but a couple tablespoons of the cheese in the center of the dough. Spread to within 1 1/2 inches from the edges. Add the caramelized onions, layering them on top of the cheese. Sprinkle with thyme.

Fold the edges of the crust dough over so that a small circle of onion is still showing in the centre of the tart. Sprinkle the remaining cheese over the top of the tart.

6 Place in the oven on the middle rack. Bake for 10 minutes at 450°F. Reduce the heat to 350°F and bake for an additional 20-25 minutes, until the crust is golden brown. Remove from oven and let sit for 10 minutes before serving.


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Showing 4 of 22 Comments

  • Jane
    The sour cream pastry was great. Instead of one large one, I use a large glass to cut circles and made individual appetizers. They were a great hit.
  • Grace

    This has become a favourite in my family after only one appearance (for my mom's 60th birthday)--and now its going to make an encore performance for Thanksgiving. I just carmelized my onions and will soon set to making my mom's recipe for a "water-whip" pie crust that we all dearly love. I'm planning to freeze it tonight (as per margaret's direction above) and then thaw it tomorrow morning and toss it into the oven in time for it to come out just before the turkey and act as our appetizer. Thanks for the new family favourite! I'm passing this one on to my kids (that I don't have yet). :)

  • JT

    Delish. Just finished and tested. Beautiful to boot. Easy. Been hankering to make this for some time. Today was the day. Definitely making for friends as a prelude to chicken marsala. Used Gruyère (missed the Swiss cheese part)...but was very tasty. Trader Joe's crust. (I put the tart on a few paper towels while cooling to drain some of the butter from the crust.) Only thing I would recommend would be to try the carmelized onions before putting in the crust and adjust to taste. Thanks, Elise...I love looking like a pro!!

  • Joan

    Since I made this only for myself as a test yesterday - I have lots of leftovers. I just popped a piece of the tart in the microwave today and all I can say is: Did I really make that? :) I don't know what it is - but the day I'm cooking, I truly have a hard time knowing the full impact of a dish's flavors. Probably comes from working with the food too much. I only wish I could eat the entire thing...right now; that good. My only concern yesterday was seeing how very rich the pastry was...But - as a treat - what the heck. My friends are going to love your recipe. You KNOW I do.

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