Cut a piece of parchment paper to fit the slab pie pan (
9 x 13-inch baking sheet). Dust lightly with flour and use it as a guide to roll out the puff pastry to size. With a sharp knife, score the surface of the pastry nearly all the way through the dough in a tic-tac-toe pattern, to mark off either 8-12 portions. Slide the parchment with the pastry into the slab pie pan and refrigerate.