Caramelized Onion Rustic Tart (Printable Version)

Flaky pastry layered with sweet caramelized onions, tangy crème fraîche, and melted Gruyère cheese.

# Ingredient List:

→ Pastry

01 - 1 sheet frozen puff pastry, thawed (approximately 9 oz)

→ Onions

02 - 3 large yellow onions, thinly sliced
03 - 2 tablespoons unsalted butter
04 - 1 tablespoon olive oil
05 - 1 teaspoon granulated sugar
06 - 1/2 teaspoon salt
07 - 1/4 teaspoon freshly ground black pepper

→ Filling & Topping

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

# Directions:

01 - Preheat the oven to 400°F. Line a baking sheet with parchment paper.
02 - In a large skillet over medium heat, melt the butter with olive oil. Add sliced onions, sugar, salt, and pepper. Cook, stirring frequently, until onions are deeply golden and caramelized, about 25 to 30 minutes.
03 - On a lightly floured surface, roll the puff pastry into a 12-inch square or circle. Transfer it to the prepared baking sheet.
04 - Combine crème fraîche and Dijon mustard in a small bowl. Spread the mixture evenly over the pastry, leaving a 1-inch border around the edges.
05 - Sprinkle half the grated Gruyère over the cream mixture. Top with caramelized onions and thyme leaves, then finish with the remaining Gruyère cheese.
06 - Carefully fold the edges of the pastry over the filling to create a rustic border.
07 - Bake in the preheated oven for 20 to 25 minutes, or until the pastry is golden and crisp. Allow to cool slightly before slicing.
08 - If desired, garnish with fresh chopped chives. Serve warm or at room temperature.

# Expert Advice:

01 -
  • It looks impressive but comes together with just a handful of pantry staples and one sheet of puff pastry.
  • The onions turn silky and sweet as they caramelize, creating a rich depth that pairs beautifully with tangy crème fraîche and nutty Gruyère.
  • You can serve it warm as a main with salad or slice it small for an elegant appetizer that disappears fast.
02 -
  • Dont rush the onions, low and slow is the secret to that sweet, jammy texture that makes this tart so special.
  • If your pastry border puffs up too much in the oven, gently press it down with a spatula halfway through baking.
  • A splash of balsamic vinegar in the last five minutes of caramelizing adds a subtle tang that really deepens the flavor.
03 -
  • Keep your puff pastry cold until the moment you roll it out, warm pastry loses its flakiness and wont puff properly in the oven.
  • Use a sharp knife to slice the tart cleanly, and wipe the blade between cuts so the layers stay neat and beautiful.
  • If youre making this ahead, caramelize the onions the night before and store them in the fridge, then assemble and bake just before serving.
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