French Onion Puff Tart (Printable Version)

Thin, flaky puff pastry topped with caramelized onions, Gruyère, and thyme—warm, savory, and shareable.

# Ingredient List:

→ Tart

01 - 1 sheet frozen puff pastry (about 9.0 oz), thawed
02 - 3 large yellow onions, thinly sliced
03 - 2 tablespoons unsalted butter
04 - 1 tablespoon extra-virgin olive oil
05 - 1 teaspoon granulated sugar
06 - 1/2 teaspoon fine salt
07 - 1/4 teaspoon freshly ground black pepper
08 - 1 teaspoon fresh thyme leaves, plus extra for garnish
09 - 4.2 ounces Gruyère cheese, grated (about 1 cup)
10 - 1 large egg, beaten (for egg wash)

→ Garnish (optional)

11 - Fresh thyme sprigs
12 - Freshly ground black pepper

# Directions:

01 - Preheat oven to 400°F. Line a baking sheet with parchment paper and set aside.
02 - Warm a large skillet over medium heat, add butter and olive oil, then add the sliced onions, sugar, salt and pepper. Cook, stirring frequently, 20–25 minutes until deeply golden and caramelized; stir in thyme leaves during the last 5 minutes. Remove from heat and let cool slightly.
03 - On a lightly floured surface, roll the thawed puff pastry to a rectangle about 10 by 14 inches. Transfer the pastry to the prepared baking sheet.
04 - Using a sharp knife, lightly score a 1/2-inch border around the edge of the pastry without cutting through. Dock the inner area several times with a fork.
05 - Brush the scored border evenly with the beaten egg to promote color and shine.
06 - Spread the caramelized onions evenly inside the scored border and sprinkle the grated Gruyère over the onions.
07 - Bake in the preheated oven 18–22 minutes or until the pastry is fully risen and golden brown.
08 - Remove from oven and let rest 5 minutes. Garnish with thyme sprigs and a crack of black pepper, then slice and serve warm or at room temperature.

# Expert Tips:

01 -
  • You get all the joy of French onion soup without the need for ramekins or broilers, and the clean-up is a breeze.
  • The pastry is so impressively golden and crisp, it always gets "what bakery did you get this from" energy—but it's quietly homemade.
02 -
  • I once rushed the onions and ended up with a pale, slightly chewy layer—patience until deep brown is truly key.
  • Swapping Gruyère for sharp cheddar does work in a pinch, but the nutty melt of the original is what feels so French-bakery.
03 -
  • Let onions cool before topping the pastry so steam doesn't make it soggy.
  • Bake on a lower oven rack for maximum bottom crispiness—it’s a game changer.
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