Caramelized Onion and Mushroom Tart
Prep time
Cook time
Total time
A super simple puff pastry tart made with meaty mushrooms, caramelized onions, and plenty of garlic.
Serves: 35 squares
  • 8 ounces white mushrooms, washed, dried, and sliced
  • 6 tablespoons unsalted butter, divided
  • 2 large onions, peeled, halved, and thinly sliced
  • 2-3 sprigs fresh thyme, leaves only
  • 2 teaspoons granulated sugar
  • 3 cloves garlic, finely minced
  • ½ teaspoon salt, plus more to taste
  • a few grinds fresh black pepper
  • 1 cup grated cheese (I used ComtĂ©, but really anything mild would work here, even cheddar or mozzarella - just don't used Parmesan as it will be too salty)
  • 1 package frozen puff pastry, thawed
  • 1 egg, beaten
  1. Preheat your oven to 400 degrees F and line two baking sheets with parchment paper. Set aside.
  2. In a large, heavy-bottomed skillet, add in 2 tablespoons of butter and your mushrooms. Cook for 8-10 minutes, over medium heat, until softened. Remove from the pan and set aside.
  3. Heat the remaining 4 tablespoons of butter in the pan with the sliced onions. Cook for 15 minutes over medium-high heat, stirring often, until caramelized and slightly browned. Add in the thyme and sugar and stir to combine. Add in the garlic and stir for 1 or 2 minutes, until fragrant, then add in the mushrooms, salt, and pepper. Stir, then remove from the heat. Set aside.
  4. Roll out the puff pastry and slice them into 2-inch squares (I used a ruler to do this to make sure they were all even). Place the squares on your baking sheets and brush the beaten egg lightly onto each square.
  5. Stir the cheese into your slightly cooled onion mixture, then place a dollop on top of each square. Bake for 25 minutes or so, until puffed up, crispy, and bubbling. When they're ready, remove them from the oven and place each square on a cooling rack, so that they're not just sitting in a puddling of grease. These can be made ahead of time and warmed again in the oven later when you're ready to serve.
Recipe by The Crepes of Wrath at