French Onion Puff Pastry Tart (Print)

Crisp puff pastry layered with golden caramelized onions, melted Gruyère and fragrant thyme for an elegant savory tart.

# Ingredients:

→ For the Tart

01 - 1 sheet (about 250 g) puff pastry, thawed if frozen
02 - 3 large yellow onions, thinly sliced
03 - 2 tbsp unsalted butter
04 - 1 tbsp olive oil
05 - 1 tsp sugar
06 - 1/2 tsp salt
07 - 1/4 tsp freshly ground black pepper
08 - 1 tsp fresh thyme leaves (plus extra for garnish)
09 - 120 g Gruyère cheese, grated
10 - 1 egg, beaten (for egg wash)

→ Garnish (optional)

11 - Extra fresh thyme sprigs
12 - Freshly ground black pepper

# Instructions:

01 - Preheat the oven to 400°F (200°C). Line a baking sheet with parchment paper.
02 - In a large skillet over medium heat, melt the butter with the olive oil. Add the sliced onions, sugar, salt, and pepper. Cook, stirring often, for 20–25 minutes until the onions are deeply golden and caramelized. Stir in the thyme leaves during the last 5 minutes of cooking. Remove from heat and let cool slightly.
03 - Roll out the puff pastry on a lightly floured surface to a rectangle about 10 x 14 inches (25 x 35 cm). Transfer to the prepared baking sheet.
04 - Using a sharp knife, score a 1/2-inch (1.5 cm) border around the edge of the pastry, being careful not to cut all the way through. Prick the inside area all over with a fork.
05 - Brush the border with beaten egg.
06 - Evenly spread the caramelized onions inside the border. Sprinkle the Gruyère cheese over the onions.
07 - Bake for 18–22 minutes or until the pastry is puffed and golden brown.
08 - Remove from the oven and let cool for 5 minutes. Garnish with extra thyme and black pepper if desired. Slice and serve warm or at room temperature.

# Pro Tips:

01 -
  • Caramelized onions turn sweet and rich, and nobody will guess how little effort it took to prepare them.
  • The puff pastry makes every bite shatteringly crisp, and you get gourmet results from ingredients you probably already have.
02 -
  • One time I rushed and didn’t cook the onions long enough — the tart was lackluster and tasted raw, so patience is everything.
  • Scoring the pastry border lightly changed everything, making sure it rises just as you want — don’t skip this!
03 -
  • Let onions caramelize slowly over medium heat — rushing this will sacrifice flavor and texture.
  • Scoring and pricking the pastry are what keep the center tender and the border dramatically puffed — don’t skip those steps.
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