Caramelized Onion Rustic Tart (Printable Version)

Rustic tart with sweet caramelized onions, Gruyère cheese, and creamy crème fraîche on flaky pastry.

# What You Need:

→ Pastry

01 - 1 sheet frozen puff pastry, thawed (approximately 1/2 lb)

→ 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 ounces)
11 - 1 teaspoon fresh thyme leaves or 1/2 teaspoon dried thyme
12 - Optional: 1 tablespoon chopped fresh chives for garnish

# How to Make It:

01 - Set oven to 400°F and line a baking sheet with parchment paper.
02 - Melt butter and olive oil in a large skillet over medium heat. Add onions, sugar, salt, and pepper. Cook, stirring frequently, until onions are deeply golden and caramelized, about 25 to 30 minutes.
03 - Roll out puff pastry on a lightly floured surface to a 12-inch square or circle. Transfer to the prepared baking sheet.
04 - Combine crème fraîche and Dijon mustard in a bowl. Spread evenly over the pastry, leaving a 1-inch border around the edges.
05 - Sprinkle half the grated Gruyère over the crème mixture, then layer caramelized onions evenly. Sprinkle thyme leaves on top and finish with remaining Gruyère cheese.
06 - Fold the 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. Let cool slightly before cutting.
08 - Optionally garnish with fresh chopped chives. Serve warm or at room temperature.

# Expert Advice:

01 -
  • It looks fancy but comes together with just a handful of ingredients you probably already have.
  • The onions turn sweet and jammy without any fuss, and that contrast with the crisp pastry is magic.
  • You can serve it hot from the oven or at room temperature, so theres no last minute stress.
  • Its one of those dishes that works just as well for dinner as it does sliced small for a party.
02 -
  • Dont rush the onions—if you crank the heat too high, theyll burn instead of caramelize, and the sweetness wont develop.
  • Keep the pastry border clear of filling so it puffs up properly and creates that rustic frame everyone loves.
  • If the edges brown too fast, tent the tart loosely with foil for the last few minutes of baking.
03 -
  • Use a really sharp knife when slicing so the pastry doesnt squash—it makes all the difference in presentation.
  • If you have leftover caramelized onions, freeze them in a jar and use them later on burgers, pizzas, or scrambled eggs.
  • Dont skip the mustard in the crème mixture—it might seem small, but it ties the whole flavor together.
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