Caramelized Onion Tart Quick (Printable)

Flaky pastry layered with golden caramelized onions, creamy mustard, and melted Gruyère in a rustic, savory tart.

# What You'll Need:

→ Pastry

01 - 1 sheet frozen puff pastry, thawed (approx. 8.8 oz)

→ Onions

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

→ Filling & Topping

08 - 1/2 cup crème fraîche or sour cream (4 fl oz)
09 - 1 tsp Dijon mustard
10 - 1/2 cup grated Gruyère cheese (2.1 oz)
11 - 1 tsp fresh thyme leaves or 1/2 tsp dried thyme
12 - Optional: 1 tbsp chopped fresh chives for garnish

# Cooking Steps:

01 - Preheat oven to 400°F. Line baking sheet with parchment paper.
02 - In large skillet over medium heat, melt butter with olive oil. Add onions, sugar, salt, and pepper. Stir frequently and cook until deeply golden and caramelized, about 25 to 30 minutes.
03 - Roll out puff pastry on a lightly floured surface into a 12-inch square or circle. Transfer to the prepared baking sheet.
04 - In small bowl, combine crème fraîche and Dijon mustard. Spread evenly over the pastry, leaving a 1-inch border around edges.
05 - Sprinkle half of the Gruyère cheese over the crème mixture. Evenly layer caramelized onions on top, then scatter thyme leaves. Finish by adding the remaining Gruyère cheese.
06 - Fold pastry edges gently over the filling to form a rustic border.
07 - Bake for 20 to 25 minutes, until pastry is golden and crisp. Allow to cool slightly before slicing.
08 - Garnish with chopped fresh chives if desired. Serve warm or at room temperature.

# Expert Tips:

01 -
  • It transforms humble onions into something so rich and caramelized, people assume you spent hours on it.
  • The flaky pastry does half the work for you, and the rustic look means imperfection is part of the charm.
  • You can serve it warm for dinner or at room temperature for a picnic, and it tastes beautiful either way.
02 -
  • Do not rush the onions; if they brown too fast, lower the heat and add a splash of water to slow them down.
  • Leave that border unfilled, or the pastry will get soggy and lose its beautiful crisp edges.
03 -
  • If your puff pastry is still a little cold, let it sit at room temperature for 5 minutes before rolling so it does not crack.
  • Taste your onions halfway through caramelizing and adjust the salt; they concentrate as they cook, and you do not want them too salty at the end.
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