Go Back

Caramelized Onion Tart Recipe

This caramelized onion tart features sweet, slowly cooked onions layered over a buttery, flaky pastry crust with creamy cheese and fresh herbs. As the onions cook, they develop a rich golden color and a naturally sweet flavor that pairs beautifully with the savory filling.
It makes an excellent appetizer for holiday gatherings, a light lunch, or a simple dinner alongside a fresh salad. The ingredients are straightforward, and store-bought puff pastry makes preparation much easier without sacrificing the crisp, golden crust.
Print Recipe Pin Recipe
Prep Time 15 minutes
Cook Time 45 minutes
Total Time 1 hour
Course Appetizer, Main Course
Cuisine French
Servings 6 servings
Calories 315 kcal

Equipment

  • Large skillet
  • Baking sheet
  • Parchment paper
  • Sharp knife
  • Cutting board
  • Rolling pin
  • Pastry brush
  • Spatula

Ingredients
  

  • 1 sheet frozen puff pastry thawed
  • 3 large yellow onions thinly sliced
  • 2 tablespoons unsalted butter
  • 1 tablespoon olive oil
  • 1 teaspoon granulated sugar
  • 1 tablespoon balsamic vinegar
  • 1 teaspoon fresh thyme leaves
  • ½ teaspoon salt
  • ¼ teaspoon black pepper
  • ½ cup shredded Gruyère cheese
  • ¼ cup crumbled goat cheese
  • 1 large egg
  • 1 tablespoon water

Instructions
 

  • Prepare the Onions: Peel the onions, cut them in half, and slice them thinly. Separate the slices so they cook evenly.
  • Cook the Onions Slowly: Heat the butter and olive oil in a large skillet over medium-low heat. Add the sliced onions and salt. Cook for 25–30 minutes, stirring regularly, until the onions soften and turn deep golden brown.
  • Add Flavor: Stir in the sugar, balsamic vinegar, black pepper, and thyme. Cook for another 2–3 minutes until the vinegar is absorbed and the onions look glossy. Remove the skillet from the heat and let the onions cool slightly.
  • Prepare the Pastry: Preheat the oven to 400°F (200°C). Line a baking sheet with parchment paper. Unfold the thawed puff pastry and gently roll it into a rectangle, smoothing out any creases.
  • Shape the Tart Base: Transfer the pastry to the prepared baking sheet. Lightly score a border about ½ inch from the edges, being careful not to cut all the way through. Prick the center with a fork to help prevent excessive puffing.
  • Add the Filling: Sprinkle the Gruyère cheese evenly over the center of the pastry. Spread the caramelized onions on top, keeping the border clear. Finish with crumbled goat cheese.
  • Apply the Egg Wash: Whisk the egg and water together in a small bowl. Brush the exposed pastry border lightly with the egg wash to help it develop a golden finish.
  • Bake and Serve: Bake for 18–22 minutes, or until the pastry is puffed and golden brown and the cheese is melted. Let the tart rest for 5 minutes, garnish with extra thyme if desired, and slice before serving.

Notes

  • Let the caramelized onions cool slightly before spreading them over the pastry to avoid making the crust soggy.
  • Keep the puff pastry cold until assembly for the best flaky texture.
  • Gruyère can be replaced with Swiss cheese, fontina, or sharp white cheddar.
  • The tart is best served fresh, but leftovers can be refrigerated in an airtight container for up to 3 days.
  • Reheat slices in a 350°F (175°C) oven for 5–8 minutes to crisp the pastry again.