In a large skillet, heat the olive oil over medium heat. Add the sliced onions with a pinch of salt and stir occasionally, cooking for about 15-20 minutes until they are deep golden brown. If they start to stick, lower the heat and add a splash of water.
Once the onions are caramelized, stir in the balsamic vinegar, mixing well to combine. Cook for another 2 minutes and then remove from heat.
Roll out the puff pastry on a lightly floured surface to remove any creases. Transfer the pastry to a baking sheet lined with parchment paper, folding the edges over to create a border.
Evenly distribute the caramelized onions over the puff pastry, leaving the border clear. Sprinkle the crumbled goat cheese over the onions, followed by the fresh rosemary, salt, and pepper. Drizzle with honey for a touch of sweetness.
Brush the edges of the puff pastry with the beaten egg wash to achieve a golden color during baking.
Bake in the preheated oven for 20-25 minutes, or until the pastry is golden brown and puffed up.
Once out of the oven, allow the tart to cool slightly before slicing.
Notes
Serve warm or at room temperature, garnished with extra rosemary if desired.
Keyword caramelized onions, goat cheese, savory, tart