Preheat your oven to 400-F and line a baking sheet with parchment paper.
Roll out the puff pastry on a lightly floured surface. You just want to remove the folded lines but keep the dough in a rectangular shape. Transfer the dough to the parchment paper-lined baking sheet.
Score a rectangular box into the puff pastry dough with a sharp knife, but don’t cut all the way through the pastry.
Melt the butter and mix it with the brown sugar, vanilla, and cinnamon. Brush the rectangle with about half the butter-sugar mixture.
Thinly slice the apples after removing the core. Toss the apples with lemon juice to keep them from browning. Arrange the apple slices on the rectangle of the puff pastry. Brush the apples with the remaining butter-cinnamon mixture.
Pinch the dough all along the edges. Bake until golden and crispy.
