Rustic Onion Tart | A Crunchy + Savory Flavor Bomb

Rustic onion tart cut into eight square pieces

This rustic onion tart brings a ton of mouthwatering flavor with minimal effort. Every bite is a seriously satisfying combination of crunchy pastry, creamy vegan cheese, and mustard filling, plus the almost meaty, savory-sweet flavor of caramelized onions. Its also very versatile – serve it with a salad for lunch (or brunch), with roasted veggies for dinner, or as a side dish in a Holiday spread.

Caramelized Onions – the Heart of the Tart

The massive flavor of this tart comes from caramelized onions. You can use any variety of onion you like – seriously, any variety will be delicious. We used shallots for the version you see in the photos. They are more subtle in flavor than other onions but tend to break down into a jammier texture when caramelized. They are also smaller, meaning you can leave them whole or halved for an interesting texture.

Caramelized onions in skillet

Crispy Crunchy Crust

We used frozen puff pastry for this recipe to keep things simple. Overall this is an easy ingredient to use. However, there a couple of things to keep in mind:

  • Double-check the package to be certain the ingredients are vegan. Many store-bought puff pastries contain dairy.
  • Make sure the pastry completely thaws before you start using it. Otherwise, it won’t be pliable and will break when you try to work with it. The best way to thaw puff pastry is overnight in the fridge. 
  • However, if you’re in a rush, you can thaw it at room temperature. Be ready to use the pastry as soon as it’s soft enough to handle. Puff pastry depends on its fat content to keep its layer of dough separate so that it “puffs up” when baked. If it gets too warm, the fat melts out, and it won’t rise in the oven.

Shaping the pastry is simple. Most puff pastry comes in a square shape, which we rolled out lengthways to create a rectangle. However, this is optional – feel free to use the square pastry sheet as is.

Next, fold up the edges of the pastry to create a shallow crust. You want the tart crust just high enough to hold in the onion filling and provide a satisfying crunch (this may unfold why baking- so don’t worry too much about being neat!).

Layer the Flavors

Ingredients to make rustic onion tart

Now come those mouth-watering flavors. Start with a layer of dijon mustard (one tablespoon), spread all over the pastry. Next, sprinkle the tart with 3/4 cup of vegan cheese. We prefer cheddar but choose your own favorite variety. After the cheese comes the star of the tart – the onions! Pile them evenly all over the base and garnish with a little fresh thyme.

Get Baked

Your onion tart is now ready for the oven. Bake it at 375F for about 20 minutes, or until the pastry puffs and turns golden brown. Once it’s done, cut it into eight pieces and serve as quickly as possible. This delightful mix of creamy cheese, sharp mustard, and melt-in-your-mouth caramelized onion is at its best straight out of the oven.

If, by some freak occurrence, your onion tart doesn’t vanish immediately, then put the remains in a sealed container in the fridge. When you’re ready to polish if off, warm it in the oven at 375F for 10 minutes. We suggest wrapping it in foil to make sure it doesn’t burn or dry out.

Rustic onion tart cut into eight square pieces

We hope you enjoyed our Rustic Onion Tart. If you try it, please let us know what you think with a comment and a rating. Every bit of feedback helps make The Plant Riot even better.

If you like the idea of more rustic pastries, check out our Tomato and Blueberry Galettes, and Spanikopita Triangles.

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Rustic Onion Tart | A Crunchy + Savory Flavor Bomb

  • Author: Rachel Steenland | The Plant Riot
  • Prep Time: 20 minutes
  • Cook Time: 20 minutes
  • Total Time: 40 minutes
  • Yield: 1 Tart / 8 slices 1x


This rustic onion tart brings a ton of mouthwatering flavor with minimal effort. Serve it for brunch, lunch, dinner, or as the perfect Holiday side dish.



  • 2 tablespoons olive oil
  • 1lb / 450grams shallots or onions, peeled and cut into thick pieces (see notes)
  • 3 garlic cloves, minced
  • 1 sheet vegan puff pastry, thawed
  • 1 tablespoon dijon mustard
  • 3/4 cup grated dairy-free/vegan cheese
  • 3 sprigs thyme, leaves removed
  • Salt and freshly ground pepper, to taste


  1. Preheat the oven to 375F / 190C. 
  2. Add olive oil to the skillet and heat the oil to medium. Add shallots/onions, minced garlic and a pinch of salt and freshly ground pepper, and cook until soft and golden brown. Remove from heat and set aside. (See notes for tips on how to keep the shallots/onions shape).
  3. Place a rectangle piece of parchment paper (slightly bigger than your baking tray) or silicone baking mat on the counter. Top with the thawed puff pastry and roll out the puff pastry to form a rectangle. Turn up the edges to help form a crust (optional). Transfer puff pastry crust to a baking tray.
  4. Cover the surface of the puff pastry crust with dijon mustard, grated vegan cheese, caramelized onions and half of the fresh thyme leaves. 
  5. Place onion tart into the oven and bake for around 20 minutes or until the pastry puff and turns golden brown.
  6. Remove the onion tart form the oven and eight pieces, sprinkle with remaining fresh thyme leaves and serve while hot! Enjoy!

Store leftover in the fridge in an air-tight container. Reheat in the microwave (30 seconds) or in the oven (350F/176C oven) wrapped in foil to make sure it doesn’t burn or dry out.


  • We used shallots for the version you see in the photos. They are more subtle in flavor than other onions but tend to break down into a jammier texture when caramelized. They are also smaller, meaning you can leave them whole or cut into thick slices for an interesting texture.
  • To keep the shallots or onions in one piece (like in the pictures), place the thickly sliced shallots/onions into the skillet and try not to move them too much. Once golden brown on the bottom, flip and continue cooking. Alternatively you can break the shallots/onions up. The choice is yours! 

Keywords: rustic onion tart, onion tart, French onion tart, The Plant Riot

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