Preheat the oven to 375˚F. Place the puff pastry on a floured surface and roll it into a 10-inch square. Press it into a 9-inch tart pan.
Coat the apple slices with the brown sugar and apple pie spice. Working from the outside edge, arrange the apple slices in a circle.
Top with cubes of butter.
Bake at 375˚F for 30-35 minutes.