Preheat the Oven: Set your oven to preheat at 400°F (200°C).
Caramelize the Onions: In a large skillet over medium heat, warm the olive oil. Add the thinly sliced onions along with a pinch of salt. Cook for approximately 15-20 minutes until golden brown.
Infuse with Flavor: Pour in the balsamic vinegar, stir well, and cook for an additional 2 minutes. Remove from heat and set aside.
Prepare the Puff Pastry: Roll out the thawed puff pastry on a lightly floured surface and transfer it to a baking sheet lined with parchment paper, folding the edges inward.
Layer the Ingredients: Spoon the caramelized onions over the puff pastry, sprinkle with goat cheese, add rosemary, season with salt and pepper, and drizzle honey on top.
Egg Wash for Shine: Apply the beaten egg wash to the edges of the puff pastry with a pastry brush.
Bake the Tart: Bake in the preheated oven for 20-25 minutes until the pastry is puffed and golden brown.
Cool and Serve: Let the tart cool for about 5 minutes before slicing. Serve warm or at room temperature.
Notes
For an eye-catching presentation, slice the tart into squares or triangles and arrange on a rustic wooden board.
Keyword caramelized onions, goat cheese, puff pastry, tart