01 - Preheat oven to 400°F. Line a baking sheet with parchment paper.
02 - On a lightly floured surface, roll out thawed puff pastry to remove creases. Transfer pastry to the prepared baking sheet.
03 - Arrange Brie slices evenly over pastry, leaving a 0.75-inch border around the edges.
04 - Heat butter in a skillet over medium heat. Add apple slices, brown sugar, ground cinnamon, and a pinch of salt. Sauté for 5 to 7 minutes, stirring until apples are tender and caramelized.
05 - Spoon caramelized apples evenly over the Brie. Fold pastry edges over the filling, pleating as necessary to create a rustic border.
06 - Bake for 20 to 22 minutes, until pastry is golden brown and Brie is melted.
07 - Drizzle tart with caramel sauce while warm. Top with toasted chopped nuts and flaky sea salt, if desired.
08 - Allow tart to cool for 5 to 10 minutes before slicing and serving.