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 time: 20 minutes
  • Cook time: 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.

rustic-onion-tart-method-1 rustic-onion-tart-method-2

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.

rustic-onion-tart-method-3 rustic-onion-tart-method-4

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.

rustic-onion-tart-method-5 rustic-onion-tart-method-6

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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Rustic Onion Tart

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Showing 4 of 24 Comments

  • Alanna

    Gorgeous … with the addition of maybe a tablespoon or two of brown sugar, this is how I cook (and cook and cook and cook) onions for fajitas. I’m curious: have you tried the Trader Joe’s pie crust?

  • Kate

    Wow, this looks delicious. Carmelized onions sell me on any recipe. Alanna, I like Trader Joe’s pie crust… actually I like almost anything from Trader Joe’s! Although, homemade pie crust can’t be beaten.

  • Ari

    Just a comment about the TJs Pie Crust – I haven’t used it personally, but I know from experience that it’s seasonal – you can probably find it now through Feb or so, but they don’t have it year round.

  • Lady Amalthea

    Oh, onions always make me happy, especially caramelized. I must try this.
    BTW, TJ’s crust is the best pre-made one I’ve found.

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