Preheat oven to 375°F. Roll out the thawed puff pastry onto a floured surface before transferring to a baking sheet covered in parchment paper. Use a sharp knife to create a 1/2 inch border around the edges of the pastry. Poke the inside of the border with a fork in several places. Spread the jam in an even layer over the inside of the border, followed by the thinly sliced brie, then the thyme (if using). Fold in each border, pinching to seal. Brush the border with the beaten egg. Bake for 25 - 30 minutes or until golden and crisp.
