Caramelized Onion Tart Quick (Print Version)

Rustic tart with sweet caramelized onions, creamy topping, and melted cheese on flaky pastry.

# What You'll Need:

→ Pastry

01 - 1 sheet frozen puff pastry, thawed (approximately 9 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
09 - 1 tsp Dijon mustard
10 - 1/2 cup grated Gruyère cheese (about 2 oz)
11 - 1 tsp fresh thyme leaves or 1/2 tsp dried thyme
12 - Optional: 1 tbsp chopped fresh chives, for garnish

# How To Make It:

01 - Preheat oven to 400°F. Line a baking sheet with parchment paper.
02 - In a large skillet over medium heat, melt butter with olive oil. Add onions, sugar, salt, and black pepper. Cook, stirring frequently, until onions turn deep golden and caramelized, about 25 to 30 minutes.
03 - Roll out thawed puff pastry on a lightly floured surface to a 12-inch square or circle. Transfer to the lined baking sheet.
04 - Combine crème fraîche and Dijon mustard in a small bowl. Spread mixture evenly over pastry, leaving a 1-inch border.
05 - Sprinkle half the Gruyère over the crème mixture. Evenly distribute caramelized onions on top, then sprinkle thyme leaves. Finish with the remaining Gruyère cheese.
06 - Fold edges of the pastry gently over the filling to create a rustic border.
07 - Bake for 20 to 25 minutes until the crust is golden and crisp. Allow to cool slightly before slicing.
08 - Optionally, garnish with chopped fresh chives. Serve warm or at room temperature.

# Expert Tips:

01 -
  • Caramelized onions do the heavy lifting, turning humble vegetables into something rich and almost dessert-like in their sweetness.
  • The whole thing comes together in an hour, which means you can have an elegant meal without the fuss of traditional tart making.
  • It works equally well as a casual dinner or something you'd serve to guests without apology.
02 -
  • Don't rush the caramelization—onions that only take 10 minutes will taste sharp and onion-y, but 25–30 minutes of patient stirring transforms them into something almost creamy and sweet.
  • If your pastry edges start browning too quickly, tent them loosely with foil for the last few minutes of baking so they stay crisp rather than burnt.
03 -
  • If your caramelized onions release moisture just before baking, drain them briefly in a fine-mesh sieve—excess liquid will make your pastry soggy rather than crisp.
  • Make the crème fraîche and mustard mixture while the onions caramelize so you're not scrambling at the end, and you'll feel like you actually know what you're doing.
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